The developers, as probable holders of large sums of Bitcoin, are invested in the optimal success of the ecosystem. This ecosystem will thrive and with it the value of the Bitcoin they hold will prosper in direct proportion to it's usefulness and adoption as a payment platform. To that end, obviously an open standard and a bazaar model will have the most powerful effect.
The only conflict of interest is one of short term gain, of potential for someone to choose to try to short change the future of the ecosystem for a very short term and limited scope profit.
I disagree. Here is an example: The Bitcoin core devs are approached by a collection of nation-states that have an ultimatum: add KYC features to transactions or we will outlaw Bitcoin. They promise to utilize the technical prowess of their collective intelligence agencies to filter network calls to the blockchain and fragment the network.
Here's the problem: core devs want Bitcoin to thrive and prosper, and even if Bitcoin can operate without the need for approval by regulators, it will stymie the growth of Bitcoin thus lowering its value... perhaps sending it into an unprecedented downward spiral. Do they risk losing all this money they made or do they hold true to the Nakamoto architecture? That's one hell of a conflict of interest.