Many of the ones you can find took no effort and are untested. A shitty script tried extracting information from a PDF datasheet or converting file formats for the purpose of driving internet traffic to an ad-riddled website.
Many are low-effort and untested. They were manually created by people who don't give a shit because they're not the ones using them.
Some are wrong. It's easy to get mixed up and number them wrong, usually upside down. Even when the issues are known, they rarely get fixed in published models and libraries.
Sometimes you need an engineered design. Pads can be designed for manufacturing, thermal, electrical, and mechanical considerations. Hardly any published pads were made by people who know how to do those things in the first place. Either way, they're not designing for your specific board.
In summary, it would be insane to spend money manufacturing random garbage from the internet, and a "good" pad may not be the right good pad for that board.
Many are low-effort and untested. They were manually created by people who don't give a shit because they're not the ones using them.
Some are wrong. It's easy to get mixed up and number them wrong, usually upside down. Even when the issues are known, they rarely get fixed in published models and libraries.
Sometimes you need an engineered design. Pads can be designed for manufacturing, thermal, electrical, and mechanical considerations. Hardly any published pads were made by people who know how to do those things in the first place. Either way, they're not designing for your specific board.
In summary, it would be insane to spend money manufacturing random garbage from the internet, and a "good" pad may not be the right good pad for that board.