Wait, didn't EA had their in-house engine Frostbite? They botched Mass Effect Andromeda because they moved from UE to frostbite (not the only reason) .

Also Unreal Engine has 24/7 support from the engineers at epic through Unreal Development Network which costs quite a bit of money.

You're right about all that.

Marketing and payroll are always the two biggest, and yes they can get to those numbers easily at AAA scale. AAA games are as big of productions as big budget movies these days. Hundreds of people involved. Graphics of that level are also extremely expensive and time consuming. Everything has to be motion captured, and the fidelity just takes a long time. Every single piece of trash on the ground has to have a full PBR material stack.

With graphics it's kind of an exponential thing. The closer you get to absolute realism the more time it takes exponentially. That's why so many indies are embracing retro graphics these days. It lets you spend a lot more time on the gameplay and content. AAAs are expected to look this good as a baseline, and that already pigeon holes a lot of design choices with the deadlines they're working with. A truly innovative game that looks AAA quality would take more years to make than these studios are willing to devote to them.

And finally there's the marketing. Mainstream casual gamers, which are who these companies are usually targeting, is the most expensive group to market to by a long shot. They can really only be reached by huge marketing campaigns on TV, social media, and physical signage. Those types of campaigns can easily get into the millions. They're also probably spending a large amount on having influencers play the game on stream. The big guys I'm sure cost hundreds of thousands, though I have no idea the actual numbers.