[chrisjj]

You can for sites that can't afford the cost of keeping up-to-date with the Google IP list without which they can lose timely indexing. That is many.

[otterley]

What do you mean by “afford the cost”? The list is free of charge (https://support.google.com/a/answer/10026322?hl=en-GB) and maintenance can be fully automated.

[chrisjj]

I mean cost of server setup and execution.

[otterley]

The server that is providing the content exists already. That's a sunk cost.

[chrisjj]

"setup and execution".

[otterley]

What serious operator of a service isn't budgeting time to implement and operate critical maintenance functions?

[chrisjj]

Me for one. Adding an auto-updating IP address blocker to my personal blog site would probably cost more than setting up the whole site did in the first place.