you can still find, download and use legacy versions of uTorrent but lots of trackers seem to not like it. qBittorrent is nicer anyway imho.
for example, when I download Ubuntu distros on old uTorrent my speeds are awful slow, but the same setup on a more recent qBittorrent build nets much faster downloads and way faster uploads. i think part of the problem is that today a lot of private tracker and a good deal of public ones don't allow users to download with older software. I'm not a web or software engineer but I imagine between security loopholes and compatibility issues they simply blacklist old clients.
shame, because the old uTorrent was simply amazing; I wouldn't go near it with a 10 foot pole now.