I'm not missing that.
You need to realize that in the AV world Crestron Digital Media is king right now with AMX trailing behind with some cool stuff as well. These two companies use HDMI right now. That could change in a few years but with the 4K transmitters and receivers being relatively new it will probably be in 2 to 5 years. This is well past the life cycle of a typical consumer laptop.
Beyond that, AV systems are not designed around professional level laptops. AV systems are designed around laptops that end users tend to bring into an office. Machines with display port are being converted to HDMI. Machines with Thunderbolt are being converted to HDMI. That is just the way it is right now. My opinion will change if and when Crestron and AMX release updated IO cards, receivers and transmitters that provide for new technologies.
In the mean time the choice of Thunderbolt 3 only on the MacBook comes off as cost savings for the manufacturer, then gouging on selling the adapters to the customer for additional money in addition to the already increased price on the laptop.
Now the users have to remember to bring a dongle. That is one more thing to forget and only serves to increase the complexity of the user experience for who are by definition as end users, typically not of a technical background. They won't think much about not having a dongle until they need it and then it will blow up in their faces. Pray it isn't a CEO looking like a fool or heads will roll.
HDMI to VGA does work. I won't go into details on the client but they where given a mandate that all C series codecs would be kicked off the network. The client purchased SX series codecs to replace their C series codecs. They are still using VGA based Enova switchers because they don't have the budgeted money to upgrade the switching infrastructure at this time. I got a SX80 to route through a VGA connection with the 15 pin connector and the RGBHV BNC connectors. So yes HDMI to VGA is possible with some caveats.
Who is talking about a world that is AV specific? Only you.
That's the point. For you HDMI is the most common. For others it's VGA. For others it's displayport or DVI. A laptop is not a wholly custom device - they have to be designed to accommodate all manner of use cases. Thunderbolt 3 today, and DisplayPort before that, is more flexible than HDMI. I never said that HDMI to VGA didn't work - only that the conversion was an active one dependent on the quality of the adapter - backed up by the paragraph you had to write to qualify your statement.