Because TV Tropes has severe licensing problems[1] - most of its content originally was submitted by its editors under a CC BY-SA license, but then the site maintainer relicensed (without permission) all its database under the incompatible CC BY-NC-SA, creating a situation where its content can't be legally redistributed.

I use adblocking so I didn't notice the ads; if you prefer, you may check it[1] at AllTheTropes,[2] the initial fork that kept the content under its original legal license. Though as far as I understand it, that project migrated to Tropedia and it is no longer maintained, which is why I linked there instead.

[1] https://en.wikipedia.org/wiki/TV_Tropes#Licensing_and_conten...

[2] https://allthetropes.org/wiki/Category:Applied_Phlebotinum

[3] https://allthetropes.org/wiki/Main_Page