As a PA (piano accordion) player I'm happy to acknowledge that in isolation, the CBA (chromatic button accordion) has many advantages and is probably a superior system in many ways.
But we play our music in the real world.
Many people come to the accordion with some "piano" skills - they therefore have a head start on PA. Paul DeBra has always been very honest on this forum about the length of the transition from PA to CBA (playing at a high level, it can be said.)
For myself, I want to keep that commonality of keyboard between accordion, piano, electronic keyboard and melodica. (Yes, the CBA melodica equivalent the "Accordina" exists, but they are very expensive.)
In some countries, UK, USA, etc, there are far more PAs than CBAs - finding what you want in the used market is therefore much easier, and there's much more fun to be had trading used instruments because they are plentiful and cheap.
There is much more instructional material available for PA in English.
The way we think about music theory in the broadest sense is deeply related to the piano keyboard, naturals sharps and flats etc.
The piano keyboard is logical and consistent - up and down in pitch are always consistent and any given interval will always be the same number of keys away. ("Black keys are your friends" - is also an important lesson to learn on the piano keyboard.)
I'll confess to being deeply tempted by CBA but I've "restarted" on too many different instruments over the years. For what I want to do, playing with and for other people, PA is the way to go.
A little more peripherally, all the accordion players I most enjoy play PA - if it's good enough for Phil Cunningham, Karen Tweed, Gordon Patullo, Alan Kelly and Sergiu Poppa, it's good enough for me!
(In countries where PA is the default, I think the "converted" minority of CBA players tend to be rather more vocal about their choice than the PA majority! Natural enough.

)
Tom