Is TKD losing popularity? The only way to know would be to see how many TKD schools and/or practioners there are today compared to in the past. So far as I know, no one has attempted such a survey.

I don't think TKD is losing its popularity. I heard that it is the most popular MA in the world, with estimates now at 70 million worldwide.

What they are losing is their credability as a MA, which I think is deserved, but sad.