1st, This is first and formost false information. It's not just luke.
see:
https://primal.net/e/nevent1qqs0qqu8j0a4kg8wpcvpfzv23tykqhh4609nnvarz0hgn3q3twmjt8sywzgqe
2nd, you entirely miss the point and make this about who develops the software, but this is myopic and irrelevant.
Bitcoin works by node runners/miners deciding what software to run.
Every node implementation can propose their own version and node runners will decide whether to upgrade or switch. That is true for bitcoin knots as well as soon as luke does something node runners disagree with. The bitcoin community is wealthy enough to fund new developers if necessary.
Thus, the steward is the bitcoin network or community at large, including bitcoin users too - and the great thing is that it is anonymously large so not prone to group think. There is no need for another layer of stewardship of tiny group of software developers. Core takes themselves way too important. Bitcoin is global and bitcoin is massive - this is much larger than the Blockstream company and always was - thinking otherwise is imho hybris to say the least.