I know people you would expect that every number has the chance of 1/20 times 70. So the most common count "should" be 3-4. But randomness doesnt really work like that with small numbers such as 70.
even now you see still differences from 470 (dice result 12) to 576 (dice result 11) although each dice result has the same chance! But still only 80% chance compared.
Here are 100000 times a d20 roll (generated with excel because the website crashes with such high numbers):
now you can see the reuslts are more like the "expected" ones. each dice number has the same chance and should average 5000 times (20 * 5000 = 100000). Still you see lows such as 4895 (dice result 19) and highs such as 5143 (dice result 6) - meaning a 95% chance compared although the "virtual dice" is not weighted at all. I just trust excels random generator here.
If you have excel here you can generate endless results for yourself:
german version: =ZUFALLSMATRIX(100000;1;1;20;1) english version: =RANDARRAY(100000;1;1;20;1)
The higher the number of rolls the lower the extreme differences get.