Getting glass hot enough to kill microbes isn't hard, but it does take a lot of energy. Microbes will attach to the glass and use that as a heat sink, so just hot water isn't enough, you have to use enough to heat the glass.

It's actually tremendously hard to do that on an industrial scale. We still get listeria outbreaks even with pasteurized milk and new bottles. Adding in a source of contaimination is going to make it that much harder.

The issue isn't getting bottles hot enough to kill germs. It's doing so in a way that doesn't aerosolize the bacteria and preventing all the other ways cross contaimination can occur.