How does DRM protect games? It doesn't, but it makes the investors of companies feel more secure of their investments.
I don't think any gaming platform should be ignored either but PC developers aren't ignoring the PC. PC games are being released, it's just that they don't take priority over the console versions since the console versions are seen as being more profitable.
However, if you're wondering why certain developers who have always made console games aren't making PC games... it's because they have 0 experience making PC games added on to the fact that they see consoles as being more profitable and secure than the PC platform as a whole.
EDIT: Also, piracy is a huge factor,.. after all, if it had no effect we wouldn't have DRM. The very idea that a company may lose a scrap of profit has made them react to piracy. That's a pretty huge effect, I'd say.