Do ISPs typically implement failover on end user connectivity?

Recently set up failover/backup cellular connectivity on my personal network.

And it got me thinking:

Cellular connectivity, or another form of dual-WAN, maximizes availability/uptime. Which is something consumers and businesses commonly really care about.

Is this something that ISPs already typically provision for end users?

If not - then why not?

Perhaps because service interruptions typically occur downstream of the ISP?

Do ISPs who pass on traffic from multiple upstream sources already exist?

Or is multi-WAN networking something that it's always the responsibility of the end user to implement?