Again, because you don't seem to be listening -- the designers design first, people vote on it last. People voting on things, or having inputs, is the last step after the designers have a crack at being creative. Psionics went through a ton of iterations -- all rejected by the users. This is not a case of restricted design freedom because they get customer feedback, because that feedback comes at the end of the design but before final polish.
And, I don't know who you're quoting there about the best products, but that's not true. Lots of truly crappy products have met needs people didn't know they had and been improved through the customer feedback loop, and plenty of great products exist that meet needs people know they have. It's a cliched statement that shows it's flaws on even the most shallow of inspections.
Psionics in 5e is not a case of restricted design. The WOTC designers were decently creative with psionics. The issue them attempting to make a "psionics for everyone" knowing that many don't care for it and still using those opinions.
Psionics being shoved into a popular opinions shows how their plan was doomed.