Because if the core devs become corrupter, the users of the community will not accept a fork to centralization. The 50 threads about block size limit changes are stupid. You've got a dozen people crying don't destroy bitcoin and they don't know WTF they are talking about.
I do know this, the people investing real money in Bitcoin related companies and technologies aren't doing it because they believe that its going to be a system that can only handle 7 transactions per second forever.
A wire transfer replacement technology that can only be used for high value transactions (because of high transaction costs due to artificially limited number of transactions) where the value following a transaction THEN has to be converted into another currency (since its now too expensive to spend in Bitcoins), is worth less than the current "market cap" of $300,000,000.00 that Bitcoin currently has.
Its not even digital gold at that point... I can trade a piece of physical gold for free.