Why the weight variances?

One thing that strikes me as quite odd is that pretty much every heavy will come into a fight at a different weight each time out.
Obviously they are concerned with being in condition and not what they weigh, but one would suspect that if training is an exact science (or should be by now) then why don't heavies scale within a pound or two at most from fight to fight?

For instance Wlad's last 6:
241.5
245.66
247.3
241.6
249
247
That's a difference of 7.5 pounds from highest to lowest.

Lennox:
256 5
249.3
246.5
253.5
249
250
A total of 10 pounds from heaviest to lightest in his last 6.

Wilder:
229
219
224
227
224
224
More consistent, but a whopping 10 pounds from lightest to heaviest in his last 6.

I remember one of the most consistent being Evander, who was 208, 208, 210, 210, 205 and then (at the time) a career high of 212 against Alex Stewart.

But here's the thing...one would imagine that a fighter who enters camp and trains for the same duration as he always does, and does the exact same thing in his training each time out, well surely that fighter would weigh within a pound or two of his previous weight each time out?

Some of these weight differences are pretty big. Okay, so we must keep in mind instances when a fighter deliberately gained weight (Holyfield vs. Stewart) or were maybe not in the best shape (Lewis in his last fight) but still, one would imagine that by now, fighters would have training and conditioning down to a fine art by now, so why such big discrepencies in the weights sometimes?
Seems a bit odd to me.

 

Yeah that makes sense but then again Wlad was 241 for Thompson the first time and 249 for him the next time. Quite a difference.
He was also heavier for Leapai than for Pulev, who was a bigger guy.

But cutting weight or adding it does make sense in that context. Here's a cookie...

 

Tyson is interesting because he came in at only 216 against the huge Razor Ruddock (2nd fight) but almost 240 (quarter pound shy) against a non-threat like Brian Nielsen.
Different periods in his career of course, but still.
But yes, to come in at over 230 was never a good idea for Tyson, who sacrificed speed and stamina as a result.