Why are movie closing credits usually animated by scrolling them from the bottom to the top of the screen? Is this because in old times there was no computer animation and the credits text template was scrolled-up mechanically by a man/device? Nowadays there must be thousands of possible ways for credit frame transitions, but still the old one is preferred.
Because this is the most natural and comfortable way of reading a vertical list of credits.
While the major credited actors/film crew can enjoy fancy transforms on their listings, it would become exhausting to see the names of rest of the bazillion film crew members to be similarly displayed.
Horizontal scrolling won't really work because someone's name/role will invariably scroll off one side before you have a chance to read it (especially when there's a full screen-full of names).
Generally, producers want you to see the full list as quickly as reasonably possible (especially as all of these people worked hard for you to enjoy that movie).