Why do affordable Wi-Fi 6 routers like the ZTE ZXHN E1600 and H3601 not support OpenWrt?

Processor: ZX279128R dual core 1GHz
Wi-Fi Chip: MT7915DA + MT7975D
Power Supply: 12V 1A
Network Ports:
* 3 x Gigabit Ethernet LAN ports
* 1 x Gigabit Ethernet WAN port
Wi-Fi:
* Wi-Fi Standard: 802.11a/b/g/n/ac/ax
* Transmission Frequency: 2.4GHz & 5GHz
* Number of Antennas: 4 (external)
* Transfer Speed: Up to 574Mbps (2.4GHz), Up to 1200Mbps (5GHz)
Security Features: Supports WEP, WPA2-PSK, WPA3, AES, TKIP encryption
Memory:
* Flash: 128MB
* RAM: 128MB or 256MB (depending on model)

I think the answer can be found here: