>> tenth marketing platform integration the engineering team will hate the marketing team

> one-time problem during setup of someone's infrastructure

As the marketer regularly making these requests, it's by no means a one-time problem, and I can attest to being hated by our tech team (for some reason they don't appreciate me hiding random JS code in our CMS to save on these requests either...).

GTM would solve many of the problems for us as we store all of our customer data in CRM anyway, but for other orgs that don't have a massive CRM policy, having an essentially outsourced data warehouse might be valuable.

I think one of the big ones is that, if setup right, you should be able to change tracking tools and not change your frontend code. They may be banking on the setup cost to be potentially expensive (engineers time) but the buyers are not in engineering (so value the engineers time highly).