When you load lots of resources from God knows where in a way such that any single failure takes the page down, you are reducing the reliability that you could have had if the resources were all in the same place which you concentrate on keeping available.

But actually, there's nothing wrong with adding dependencies, granted that you correctly do your risk assessment. Are those developers assessing their risks and making an informed decision to add them?

I'm really starting to doubt whether it's competitive to do your own thing anymore. And this seems to be getting worse.

Hard to compete with the combo of features & scaling that cloud provides. Attempting it pretty much guarantees you a gnarly trade-off somewhere (reliability, complexity etc).