When I try to download GTK, I get redirected to a Sourceforge page containing a personal data form. It claims the download will start presently, but it doesn’t. That doesn’t happen with the other apps. What’s up? Look suspiciously like a scam.
Sourceforge sometimes puts up adverts that look like they are for (or are close to) the application you initially requested. If you mistakenly click on the advert, you could be taken somewhere else entirely. Make sure you click on the ‘skip this add’ or wait for it to time out, or look for the ‘direct link’. Annoying, but I guess it pays their bills.