This data is presented in a really frustrating way.

First, I suspect (but I'm not certain) most companies do it as X% of salary. So I have no idea if I'm looking at truly different on-call policies or rather salary spreads.

Second, there's no associated estimation of how much work "being on-call" is. For us, a small team with SWEs doing voluntary on-call, any out-of-hours page is immediately top priority for work the next day. The person on-call also gets the final say over risky deployments after lunch / on Friday. I know that's not universally true, and we've worked with companies that consider a page a week or even more normal (still without a separate SRE/OpsEng team). If any of us was getting paged once a week, we'd refuse.