it's a mixture of

1. easy wins for politicians in conservative areas of "won't somebody think of the children?!?!" so they can look like they're doing stuff to stick it to big tech while appealing to their voters' sensibilities

2. wanting to de-anonymize the internet as much as possible in the name of CSAM and anti-terrorism but is actually about wanting unchecked surveillance. the same reason we have to bang the drum against anti-encryption laws that they try to pass every several years