I doubt eBay was originally built with PHP - when it was founded in 1995, the very first PHP version had been available for barely 3 months. I expect the original EBay was mostly Perl, which was the standard at the time.

The others I don't know, but MySpace was not a particularly big operation. Before WordPress, most sites started as PHP at some point were expected to migrate to something else, because maintainability of PHP3/4 projects was a big challenge (hence the "shame"). Facebook was the first company that simply refused to do that, and focused on improving PHP instead.