-0 is not less than 0 or +0, both -0 < 0 and -0 < +0 returns False, you’re mixing the behavior of Math.min with the comparison of -0 with 0/+0.
The specification of Math.min is clear on this point:
b. If number is -0𝔽 and lowest is +0𝔽, set lowest to -0𝔽.
Without this exception, the behavior of Math.min and Math.max would depend on the order of arguments, which can be considered an odd behavior — you probably want Math.min(x, y) to always equal Math.min(y, x) — so that might be one possible justification.
Note: This exception was already present in the 1997 specification for Math.min(x, y), so that’s not something that was added later on.