The /tp command, when used with relative coordinates, changes the position or rotation relative to the client, but the /rotate command seems to set the rotation of the client to the result pre-calculated on the server.

The problem is that, when /rotate is runned every tick, it makes the client's camera movement jittery. Try running the following command with a repeating command block.

execute as @a at @s run rotate @s ~ ~ 

Then try moving your camera around. You can notice that the movement is not smooth, and it is hard to move. This does not happen when you use /tp instead.

execute as @a at @s run tp @s ~ ~ ~ ~ ~  

The problem gets worse if you're in an environment with high ping.