Both views are correct. Many are building b/c it's the only way to get an EV, and they're tired of/disappointed with the broken promises of the auto industry....
One view is that most people who build an EV do it because that is the only way to get an EV, and the availability of vehicles such as the Nissan Leaf would put an end to the practice.
The other view is that mainstream acceptance and awareness of EVs, along with charging infrastructure, etc, will actually help the DIY EV market grow more.
OTOH, many build b/c they like the process or the mainstream will never produce the vehicle they're looking for. Look at the Experimental Aircraft Assn. and how its grown, especially in the last 20 yrs. They're building vehicles way cheaper and often much more capable and advanced than the production vehicles.
Mainstream acceptance will greatly enhance availability of infrastructure and quality of components while lowering their cost.
I view the current homebuilt EV movement in much the same way as the PC movement of the 1970's/80's. They too were initially hobbyists, but we've now hit critical mass. EVs, being largely driven by electronics (pun intended), are experiencing Moore's law. Battery/storage technology, in particular, will double capacity while decreasing volume & cost every 18-24 months.
This is just the beginning. Ladies and gentlemen, fasten your seatbelts and hang on tight - you're in for an electrifying ride.