The buttons are prominently there to meet ADA (Americans with disabilities Act) or ACA (Accessable Canada Act).

Buttons at intersections help people with mobility issues to cross at dedicated crosswalks or crossways safely, most buttons extend the cross time when pressed.

For people that have visual imperments the buttons will generally activate a chirp sound, which helps with a "haptic feedback" of where crosswalks might be or in which direction to proceed.

Anyways, they have become so ubiquitous that they are pretty much expected everywhere, so much so that people don't see them as accessible infrastructure (which is a pretty good thing TBH).