most of the website has some level of commerce today, but I don't see there is enough commerce support in the backdrop now, commerce, stripe, paypal all these basic plugins are MUSH have for most of the website.
Ubercart is a very complete solution that is available on Backdrop CMS. It also has Stripe, PayPal support.
Also check out this forum post that lists several other solutions:
The big one that's not (yet) ported is Drupal Commerce
Ubercart is an excellent solution, I'm using it on a few website.
Out of the 170+ websites I look after only a handful of them need e-commerce in any shape, way or form, so your comment isn't really accurate unless you mean the websites you look after and not websites in general.