Why are autoloading tanks generally fast?

Lert: Because 'autoloaders' (wrong term really, but nobody seems to care) were a design fad in a time where the IRL tank 'meta' was shifting from slow, thickly armored machines to fast, thinly armored ones. Post WWII they found that ammunition and gun technology had outran armor technology, so the design meta shifted to tanks that found defense in not getting hit, rather than in shrugging off hits. Re: Leopard 1 et al.