However, it's not GTM's fault, at all. GTM gives marketers a very powerful suite of tools that they normally have to rely on devs for. In fact it gives them site-breaking power.
But it's not GTM's fault a marketer can't track a button click in the scenarios. The marketer just needs to push the responsibility back to the dev who made the crummy site. GTM can't help if a site is built in an opaque manner. GTM can't help if a marketer can't learn to use it competently either.