Do they fit? Or do they only seem to fit because we're so used to them being there? Tigers and onions don't really have anything to do with a factory that manufactures bombs (nor do they have much to do with many of the other environments in which they've appeared over the years).

Pre-SNES Bomberman games largely just had random animals and strange monsters with little in common with their environments. They were very abstract things like blobs that cry when you blast them or frilly mouths that chomp repeatedly. Bomberman '93 and Bomberman '94 were taking the series' very first fledgling steps into more diverse and structured design, with enemies that were actually unique to certain worlds (and which fit thematically), big bosses that stretched over the screen, and by the time Bomberman '94 appeared, even traps that play into the worlds' environments.

If you look at Bomberman, Bomberman '93, and Bomberman '94, all for the PCE, each released sequentially, you can really get a feel for how these older games were still trying to cling on to the style of NES Bomberman, but were gradually adding and revising elements to refine the gameplay and general aesthetic.