Ebm seems to be the only one offering 30m in limits. Most others are up to 20m.
In 99.999999999999 percent of situations $20m should be more than enough, but some people might be prepared to pay a bit more to get the higher limits.
What kind of claims could be worth more than 20m?
A very very nasty liability claim involving injuries to a minor who may need medical treatment and care for rest of life ... No one wants that to happen