[apabepa]

Yes the ads/trackers/etc is most likely a reason that a webpage cannot be completely without javascript.

Two other possible reasons from the top of my head:

If a web developer is hired to make a site they can probably charge more if it is a fancy javascript site. In some cases it might be in their self interest to up-sell this to a client that does not know better.

If a web developer makes a site for themselves I am sure many want to take the opportunity to get some experience in the latest web-tech while they are at it. Just as I will use an obscure programming language for my next side project..