Why does our number system have only 10 different symbols?

Question

To be specific, I am just curious as to why does our number system have 10 different digits?Just for an example, why did it not end at 7? (it is the greatest prime number before 10, there are 7 days of week). Or similarly any other digit
If we assume the digits were derived from the number of fingers(including thumbs) on our hand, then why is it so that 0 represents nothing, 1 represents one finger, then for the 10th finger, we don't have a unique digit, but have to ADD one more to nine.

EDIT: My question also aims to clear one more thing. If it is derived from the number of fingers, then why don't we have a special symbol for the 10th finger,

Answer 1

If I show you both hands two times and then three fingers, I show you a total of $23$ fingers, where the $2$ and the $3$ excellently represent the two double-hands and the three fingers. Likewise, one double-hand and no extra fingers should therefore be represented as $10$, not with yet another digit.

Answer 2

Prime numbers are not really convenient as bases for number systems. There is rather an advantage in having divisors, which is likely why some other number systems where based around $60$ and $12$ is a also common (recall a dozen, and the timescale).

The reason for base $10$ being the ten fingers is plausible, the fact that it is a kind of convenient size and has some divisors might have contributed to it.

The reason why ten fingers lead to base ten rather than to base eleven is nicely explained in the other answer.