Just because SOME ASNs don't have it in place doesn't mean it's not uncommon. In the link provided, 80% of all tracked network blocks for ipv4 are blocking spoofing. Though they only track 1000 ipv4 /24 blocks and their data is highly biased towards having spoofable ranges, considering their end goal is identifying spoofable networks!
Just because SOME ASNs don't have it in place doesn't mean it's not uncommon. In the link provided, 80% of all tracked network blocks for ipv4 are blocking spoofing. Though they only track 1000 ipv4 /24 blocks and their data is highly biased towards having spoofable ranges, considering their end goal is identifying spoofable networks!