ELO isn't a bad band at all, IMO, but in fact represents exactly the caliber of band that I think needs to exist *outside* the R&RHOF in order for it to have any credibility. As long as there is a tier of good bands that existed for a number of years, had multiple hits and multiple big-selling albums and some critical acclaim but which *aren't* in the HOF for one reason or another, the Hall can at least maintain a shred of an air of exclusivity.
The only qualification for getting into the HOF now is some base level of popularity in their day and having maintained a decent fanbase in the present day. That's it. That's the only explanation for why Green Day and RHCP could be in the HOF, and for why the HOF is now reaching back to seize on any '70s band with a pulse instead of inducting more deserving of their contemporaries.