Sorry, typed that in a rush. Here's a response that actually makes sense (maybe).
In mobile, Opera is already a Big Thing. There is somewhere to go *other* than up. Would they really want their hypothetical future competition advertised alongside them? Firefox, various and sundry WebKit browsers, etc.? Opera isn't on there by default, no, but it's not exactly unheard of either.
I guess it's a tough choice - stay a decent size with little real competition or gamble that in an attempt to get big...