In the corporate world, they have a lot to lose. So, they have lawyers - expensive lawyers - who, in theory, protect them from expensive lawsuits. One of the easiest ways to stay out of lawsuits over GPL and friends is to not use GPL software, so... that's why it's radioactive. Just having the parasitic lawyers review possible exposure is hellishly expensive, better to re-develop in-house than pay lawyers or even begin to think about the implications of entering into an agreement with a bunch of radical FOSS types.
It sucks, but it's also how it is. Some corporations (like Intel) do heavily support and contribute to FOSS, when they feel like it.