Two issues at play
1) Functionality.
Mechs are not regulated, as you point out. For some, this is a blessing and allows more freedom in build config, particularly when it comes to volts/amps/watts. They are also less prone to failure. PCB's fail. Internal batteries (not in the vamo, I know) fail.
For mech fans, the vape consistency issues with a draining battery are more than compensated for by these features (or rather, lack thereof).
2) Price.
Some mechs are considered exotic collectibles and have prices to match. Others are very reasonably priced - going the clone route can get you a good mech for the same $35 you paid for the vamo. Some low end authentic mechs can cost that, too (and just to compare apple to apples, the vamo is generally considered a good low end APV - check out the prices of DNA30 devices like the Vapor Shark, for instance).
Still others, such as the reo, are "higher" priced, but worth every penny considering the effort, quality of workmanship, and support. Not for everyone, sure, but they are so very much more than just a switched DC circuit in a box.