Because my PC isn't meaningfully more secure.
Because in the overwhelming majority of situations, if that security is compromised, my bank will eventually cough up my money.
Also because I also expect neither Google, Apple, my carrier, nor the dab gum gubment is likely to rob me by...
*checks notes*
Compromising the banking app on my phone. Or my PC. Or my router. Or any of the other non-100% secure devices and processes I use to get through my life.
There's basic security precautions, and there's living in fear and paranoia, brought on by a misunderstanding of the threats you are facing.