There's some commercial software to sell/resell VPS, etc that some of these outfits use.
And it's pretty much a commodity business, so things are going to tend to look similar. If you're buying $5/month VPS, you don't want to pay for a lot of fluff. A lot of these are small time local hosters in a single location, but that's usually all you need for a small site.
Its usually WHMCS + virtfusion
There are alternatives but usually all just go use these for some reason
This is also why a lot of these websites might look similar as well.