Because that is how Bluetooth is specified. Bluetooth is primarily used for audio, where high throughput is not the most important parameter. Expected Bluetooth throughput is less than 2 Mbps, see more here https://www.bluetooth.com/blog/exploring-bluetooth-5-how-fast-can-it-be/

WiFi on the other hand, has peak throughput above 1 Gbps. So your observations are as expected.

Apropro WP: https://lemmy.world/post/6582047

How do you enable swipe back?