>>38218066Because Normal attacks are kind of useless outside of them having really high base power or a really good secondary effect? Which Tri Attack sort of does with the decent chance for status, but eh. A STAB Flying move with the same base power is generally more useful since it can hit some things for super effective damage. But as Dodrio's options for moves are pretty limited in gen 3, you'll probably want to run a Normal move anyway alongside it so if you don't want the raw base power of Return you can pick Tri Attack instead.
Doduo and Dodrio are some of my favourite Pokemon, and are also the superior choice of Normal/Flying in gens 1&2 over Pidgey, Spearow and Hoothoot. Even if you only get them later on.