Tor is like a VPN but sends your traffic through multiple servers (so that no single server has all the information).
The Tor Browser also has great tracking protection: it makes it very difficult for websites to distinguish you from other Tor Browser users and makes you look different everytime you restart the Browser.
I am not sure but i can imagine the following reasons:
You do not want anyone (like your ISP) to know that you use tor (to avoid being flagged as suspicious). They will only see that you use a VPN.
Tor is blocked but the VPN not
You do not want the Tor entrance node (the first server in the chain) to see you IP (The entry node only knows your IP, the middle nodes knows nothing (only forwards encrypted traffic from one Tor node to another) and the exit node only knows what websites someone is connecting to but has no idea who that is)
doesn’t tor do just ip spoofing?
Tor is like a VPN but sends your traffic through multiple servers (so that no single server has all the information). The Tor Browser also has great tracking protection: it makes it very difficult for websites to distinguish you from other Tor Browser users and makes you look different everytime you restart the Browser.
and why do people use both?
I am not sure but i can imagine the following reasons: