More often than not, it's not ISPs ignoring TTLs as you describe, it is an improperly configured SOA record. There's more TTLs you (as owner of domain) control

More often than not, it's not ISPs ignoring TTLs as you describe, it is an improperly configured SOA record. There's more TTLs you (as owner of domain) control involved in the caching of a record than just the TTL on an A/AAAA record. As to your point about "propagation", argumentum ad populum applies.