Opensubtitles became really frustrating to use once they began asking for a login and a password to download subtitles in VLC or Xbmc/kodi (basically every time you need to use the API). I always forgot about login details and in my opinion it wasn't needed at all for them except for profile tracking I guess. They forced people to register to get subtitles, they willingly forced people to increase their attack surface for not much benefits to users (and probably themselves).

edit: at the time I also was young and naive [0] and thought the open part of opensubtitles meant that people submitted subtitles in their free time out of their good heart and the site was simply hosting and organizing them, no problem with displaying ads on the website or at the beginning of the subs I thought, to make up for hosting costs. Subs hunting was so much fun at the time /s. But having to register to "prevent abuse" was a tad too much.

[0] still am by the way, thanks for asking :)