Why does one side of the accordion have one type of keys and the other has another type of keys?
If having this many button keys is a possible/valid thing, why not have a lot of small round keys at both sides of the accordion, instead of a lot of button keys at one side and fewer piano-style keys on the other side?
Chromatic button accordions exist. Large instruments (like Russian concert bayans) have 64 different notes on the treble side, as opposed to the 45 note maximum for large converter piano accordions.
Amateur accordion ensembles tend to have a significant ratio of piano accordions, conceivably due to the considerably tighter relation between scores and piano keyboard. However, folk music ensembles in countries with significant button accordion tradition (Finland, Russia, Serbia, France, Belgium, partly Sweden, Italy, Portugal and a few others) where players tend to play by ear very often use chromatic button accordions, and several countries have their own "native" style of such instruments with particular layout, size, and visuals.
Accordion solo competitions tend to be dominated by chromatic button accordions: for intensive players, the technical advantages of chromatic button accordions compared to the piano accordion layout tend to pay off. For amateur players investing a limited amount of effort, the tradeoffs are less clear, and local availability of teachers and (particularly preowned) instruments significantly governs the choice of instrument type.
