Wifi Tx rate in airport and speedtest cli upload/download speeds are drastically different

When I run airport -I or opt click my wifi icon, it says my wifi Tx rate is around 700 Mbps, but when I run the speedtest-cli command, it says my upload speed is 20 Mbit/s and download speed is 30 Mbit/s. Shouldn't the upload speed and Tx rate be the same thing? What is the difference?

Tx rate is the speed of connection between your computer and the WiFi; this is not the same as the speed of your network connection provided by your ISP. So you might have a high speed in your local network, but accessing the internet has lower speed limited by your internet plan (which is what speedtest-cli tests for as it establishes a connection with a server somewhere else).

If you want to test LAN speed, use iperf on local devices.