Joins in with Woody (standing and waving), count me in that mess!
The thing about any serious custom project, especially a scratch-built vehicle, is there are just a tremendous amount of decisions to make. As I'm sure Woody, and the other scratch-builders here, can attest to - just getting to the point where you know what you really need/want to build for a chassis can be like climbing a mountain. Every decision leads to ten more... That's before you ever throw the first spark. Unless you're building an exact replicar, clone, spec-class racer, or something otherwise pre-determined, that process grows exponentially as you build. Most people simply don't have the time and/or finances and/or patience to become that involved.
I think it's also easy for people to underestimate the time, money, design, and engineering that goes into a standard production vehicle. Honestly, most modern production vehicles are hard to beat. So, when you do a conversion, you take advantage of millions of dollars of development work. The challenge is just to do the best you can to make the EV conversion a seamless part of the original vehicle. That can be a serious challenge in itself for even a decent custom or conversion shop.
I've seen many custom vehicle projects, based on production vehicles, over the years I've been in the industry that resulted in almost immediately dissatisfaction when the owner finally got to enjoy them. It's easy to make a production vehicle feel, handle, and ride like a pile of crap - much easier to build a pile of crap from scratch. That makes a conversion an easier risk to swallow.