Slightly more difficult, slightly more expensive, slightly more complicated to interact with, slightly more confusing, slightly harder to sell its merits… a lot of slight annoyances compounding eventually can make any product not appealing for R&D, and not worth trying it to get off the ground. The neat part is that in most cases you don’t even hear about these projects, because they never materialise. Maybe that’s why we never saw any such protocol being developed before the exploit of the Taproot hack.