The V1 decision speed is not fixed, it's calculated for each take-off based on weight, wind, runway conditions, maximum thrust settings etc.
It meets these constraints:
1. Low enough such that if you try to stop from that speed you will stop before the end of the runway
2. High enough such that if you have an engine failure at that speed, you will make it airborne on the other engine before the end of the runway
3. Not higher than rotation speed (you can't decide to abort after pitching the nose up and getting the aircraft airborne)
4. Not lower then minimum control speed (you can't keep directional control in case of an engine failure below minimum control speed, so your only option is to abort)
If there is no speed that meets all conditions, then your runway is too short and you can't go. Reducing weight helps, since you'll accelerate faster, stop easier, and take-off at a lower speed. So that's usually the solution if your runway isn't long enough.
Constraint 1 is why you're committed to takeoff above V1. If you would try to stop above V1 there is no guarantee that you'll stop before the end of the runway. While you are guaranteed to be able to take-off above that speed, even after an engine failure. So you take the problem into the air, run checks, and return.