Warp factor is basically a measurement of speed that created by human or other species on Star Trek (in universe explanation). It is the same as our current measurement of speed like km/hour, miles/hour, etc. So why do we make an infinite speed at warp factor 10 and not warp factor 100? It just like that we (the in universe scientists) make it hard for themselves.
Because as the chart works, when you reach warp ten, you've reached infinite speed; the amount of time and distance traveled becomes everything (for lack of a better descriptive phrase).
Warp chart:
http://memory-alpha.wikia.com/wiki/Warp_factor
It is the same as if we decided to consider 100 miles / hour as an infinite speed that impossible to achieve.
No, as pointed out, it's distance covered and speed. Imagine you had a speed chart where Speed 99999.9 took you across the Earth and back to where you started in something like 0.00001 seconds. Then you reach Speed 10 and you literally arrive at the same second you left, effectively never leaving, you moved so fast. This could probably be described better by somebody else.
I think TOS measure of Warp factor is more rational than how TNG measure the Warp Factor. Warp is only a measurement of light speed. It is human who decide how fast is Warp factor 10.
Nah,
TNG nearly cleared it up and made it better for factoring warp speeds.
So infinite speed can be marked as warp factor 10, warp factor 100, or even warp factor 1. It's all depend on us.
But at that point you're not arguing one can go faster, since you're already at
infinite speed, you're just arguing over the number assigned to it, so it's rather meaningless.
So why warp factor 10 have to be infinite, and impossible to achieve?
Trek is like real life -- not everything is possible, even in the 24th century there are things they struggle to achieve, plus it would suck as a viewer if you could just go anywhere instantly. Not only does that remove drama and interactions in-between, but it eliminates pointless fun warp chases.
But it doesn't make the speed impossible. I'm sure somewhere down the line in 25th century, they can go infinite speed. But it's really not needed. You can get so close to infinite speed in factors of upper warp nine, that you're basically only wasting hours if not days instead of an instant.
I watched the Voy epsideo Threshold. And I think capt Jeanaway and her crews are all idiot!!!! That warp factor 10 shuttle was a success experiment. It can go at warp factor 10 (that basically has infinite speed that can reach everywhere in this universe in an instant).
So what if it's dangerous for human? It can always go to Federation space in an instant without any human inside it. Just send it back to federation space without any human or Vulcan or others inside it. Use it to bring message to the Federation about their condition.
Or, they can just move at warp factor 10 to the Federation space with Voyager. Why do they have to care about evolve to reptiles. The doctor can turn them back to human in an instant. Look at Janeaway and Paris? They turn back into human aren't they? So the experiment was a success. They could finish their mission after that episode. But they didn't. So they're idiot.
Because Janeway liked to torture her crew. It's a proven fact. ;-)
And the writers hated us just as much.