This is entirely speculations but I think that may come from a very interesting factor - it's not what the engineering team views as a core competency. There may be a big divide in how the business is perceived between marketing and devs and optimizing Ads (this throw away side-component) isn't viewed as a tech priority by the team.

A more reasonable reason might just be that trying to be a platform of everything is a complex proposition and they've accepted so much complexity that all their labour at this point is being poured into maintaining that complexity rather than making improvements.