A possible explanation why typos for major sites are sparsely registered could be that the domain industry has put a lot of focus the last decade on addressing malicious registrations, and many registrars that focus on the market segment of large companies sell products that monitor for malicious registrations with legal response in case one pops up. It is also seems that bulk registrars has gotten better filters to reduce malicious registrations, which is a service some security companies offer to registrars. In theory it should be quite more difficult today for a malicious actor to go to a major registrar and buy an obvious trademark infringing domain for a major site.
Domain/trademark monitoring also directly compete with defensive registrations. Often it is a question if you want to pay the lawyers/monitoring service, a large number of registration/renewal fees, or both.
My guess is also that not all typos are equal. Should have a stricter edit version for 1-keystroke-away filtered edits (that is delete, swap or add 1 key away / replace one key away) instead of pure Levenshtein. Like Fqcebook is a more likely typo than Fjcebook but they are both edit-1
Domain/trademark monitoring also directly compete with defensive registrations. Often it is a question if you want to pay the lawyers/monitoring service, a large number of registration/renewal fees, or both.