It's an IoT device, not a laptop. It does not really need 5ghz to fulfill its purpose as an embedded CPU, and adding 5ghz likely would require making some room for it by removing other functionality.
Yes and in some uses cases it works against you. 2.4 is incredibly crowded without adding 802.11 to the mix. My IoT admins would have less complaints if they could take advantage of my small cell 5Ghz spectrum. This isn't 2005 with widely deployed asymmetrical wireless networks.
I use ESP32s extensively. I also use wifi extensively around the house - I have about 8 wifi access points around the property, with a ton of commercial IoT stuff powered on including sensors, lights, cameras, you name it, I got it. It's about as wifi-congested as any house can get.
So, I was measuring about 250KBit/s on an ESP32, and I decided to test everything that might increase the speed. I tried all the available antenna options for the ESP32 including many exotic antennas using the IPEX antenna connector variant of the ESP32, the stock ESP32 pcb antenna, and several chip antennas. A couple of them got up to 300KBit/s.
I also decided to see what happens when I power everything else off except for a single wifi router. So I did that, and I found that the stock ESP32 pcb antenna still got only 250KBit/s, and the other antennas measured exactly the same as they did before shutting everything down, too.
So, I don't know... 2.4ghz seems fine to me from my anecdotal tests.
Can't you just underpower the antenna on a 2.4 radio if you need networks that don't bleed into each other as badly? Unless it's an issue because of the tiny antennas that usually come on microcontrollers.
True for devices under your control. But think venues with large BYOD counts. Add in that all client devices generally transmit at full power. End result is an environment with not a lot of headroom in the 2.4 space.
2.4ghz isn't the only problem - even cell towers have problems with large amounts of devices. And "large BYOD" events are not a normal use case for wireless, and even 5GHz will have problems in those situations.