In my very limited experience, this is common even for real business customers. I think it's because going from commercial ISP service to BGP service is not really an upsell. It's a completely different product category (carrier interconnect) and usually results in less revenue for the ISP (greatly reduced bandwidth charges etc.). As a result, sales folks aren't trained on it, and it is difficult to get through regular channels.
If you get it, it can be great. Imagine your ISP calling you when you reboot your router.
I'm running BGP to the home, over wireguard, from a couple of VPSes. It wasn't worth it to upgrade to DIA for me. It's mostly for hobbyist purposes so reliability is not really a huge factor.
If you get it, it can be great. Imagine your ISP calling you when you reboot your router.