The ones with an aluminum tonearm definitely do have a spring to set the tracking force. I know because I just modified one recently to increase the spring tension to get it down to its minimum spec of 4 grams. (There is no thumbscrew to adjust it like on old BSRs, but you can adjust it by carefully unhooking the spring and re-hooking it on a different loop.)
The
really cheap ones with an all-plastic tonearm don't have a spring or counterweight, because the entire weight of the tonearm and cartridge is 5 grams, right in the middle of its recommended range.
How did you measure it? If you placed a scale on top of the platter, you did it wrong.
I demonstrate it here with a Pioneer PL-990, but the concept is the same with any turntable that uses a spring-balanced tonearm:
Incorrect -- scale on top of platter:
Correct -- scale at same height as the playing surface of a record: