In the US, the majority of MSE walls with panels and steel reinforcement are for state and federal transportation departments who determine what kinds of retaining walls are required at a location prior to bidding based on geotechnical, structural, aesthetic, and cost requirements. In most cases, this is determined by a geotechnical investigation that considers bearing capacity, settlement, and global stability issues with the proposed forms of retaining wall construction. In simple terms, they attempt to not specify or consider systems that will not work properly at a given location for geotechnical or structural reasons. An example would be to not consider MSE walls where insufficient space exists for their installation or a location where any gravity wall would slide down a hill without considerable subgrade stabilization.
However, there is a segment of transportation projects that are classified as design-build where the design-build team has responsibility for all facets of the project and will have to divide up the responsibilities for things like global stability among the team members. In almost all cases, the geotechnical engineer is the most qualified to do this work since they are in charge of the geotechnical exploration program and will determine what exploration and testing will be done.
The US private sector is completely the opposite of the transportation sector and everyone tries to pass responsibility down to the lowest levels on a project so that a person with a tractor is responsible for getting global responsibility checked on a wall he is building. Of course, there are no borings taken in this part of the jobsite since the geotechnical engineer was never retained to do any more work than the initial investigation where structures were not yet identified (I am being kind here to low bidders).
Back to the OP, proprietary wall systems (panels, blocks, etc) typically design their components for a given project but this requires a lot of trust. Specifications are necessary to determine for example the concrete used in the panels if the owner wants a strong and durable concrete panel. It would be like asking for a design-build driveway and not specifying the concrete material and letting the contractor choose for you. It all looks good for a year or two but what about 10 or 20 years? The same holds true for many aspects of the MSE wall design, you should understand all the key elements to be able to specify then check for conformance to whatever standards required or specified.