Likely desired height of propellers above the ground (aero, damage, clearance, etc) combined with fuselage size.

they want a low cabin (step into, like a car) and maybe (like in the last pic) they don't Have to do VTOVL so the wing needs prop clearance. If they Had to do VTOVL (as shown, like there's an inter-connect between LG extended and props horizontal) then not needed

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

Every picture you've posted shows props that cannot fit in an underwing configuration.

A more obvious issue is that military VTOLs can't always afford to spin down the props to disembark troops, so how are they to safely egress with spinning blades a few feet off the ground, not to mention the severe side-wash from the props spinning so close to the ground.

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Mainly clearances. These are small aircraft, and the passenger circulation right outside the cabin is limited, so there are potential hazards like hitting the head with wing, booms, pylons, etc.

One engineer mentioned that Joby adopted the gull wing to reduce interference drag between wing and fuselage.
Is it right comment?

gull wing does have some aerodynamic advantage, but as shown it's mostly the desired wing plane didn't fit with the fuselage.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

I don’t think these eVTOLs are designed to fly fast enough to make drag a significant consideration for the wing root shape, but I’m not an aero guy.

Remember, none of these are mature designs.
Keep an eye on CityAirbus if you want to see a more developed project.
You will also notice that CityAirbus is talking about much less range and speed than the rookies are.
Most of the info out these on these does not take into account reserve margins, diversion requirements and battery degradation.
There is a lot of work to be done on these.

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P.E. Metallurgy, consulting work welcomed

EdStainless, what aspects do you see that are not mature? Archer and Joby are about to be certified after years of R&D. The engineers that are working there are excellent and brought their experience from other OEMs from all over the world. How more mature a wing/fuselage, empennage design needs to be?

They are about to start full scale testing.
As of today most of their sub systems aren't certified for flight, and neither is their airframe.
Their PR is for attracting investment, not stating the honest performance of the system.
The range and speed are just one part of this.
Just look at the numbers they say they will be building.
They expect to ramp up to hundreds of units a month within a year, all while meeting FAA requirements.
I'll believe that when it happens.

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P.E. Metallurgy, consulting work welcomed

yes, they may be good technical designers (so were the Brits), but that doesn't make a market success.

the business plan ... not too ambitious, but also not too cautious.
the manufacturing plan ... keeping costs down, controlling configuration ... offering a range of configurations, but not too many.
the politics, the world economy, the original idea (is there really a need for these things ?), all the myriad of design trade-off decisions made during design.

There are a few examples of planes that became successes (747, Bombardier RJ, 737, A320) and there are many more which, despite being good designs, failed in the market.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

EdStainless all those points you're mentioning have nothing to do with a mature design. Joby wing design is mature. All aircraft manufacturers go through those processes to get certified. And companies as Boeing or Airbus have been struggling through that process as well. Aircraft design and certification is one of the engineering challenges more complex in industry.

Also market success has nothing to do with a mature design. The A380 is a magnificent engineering program, but market was not for it.

at some level, an airplane isn't mature until it's been in service for several years, and had it's teething problems sorted out.
at some level, a design can be mature in that the design is not evolving in any major way, that the big design decisions have been made (high wing, tractor props, MTOW, power plant, etc).

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

rb1957 but here we're talking about the wing design, a wing design is mature in terms of configuration for the certification model. The wing design will not change after entering into service and probably the whole life cycle of the aircraft. Few tweaks might see afterwards, but the skins and bones are a baseline that will not see radical changes. The wings of the Joby and Archer aircraft are a mature design

just saying there are a couple definitions of "mature". But we're picking away at a single word on a post (and not talking to the OP's question).

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.