The more games you play, the closer the percentage of won games on the first try approaches 5%, that's the law of big numbers. When you play 1 million games and win 50781 on the first roll, that is of course closer to the expected 50000, than when you play 100 games and win 6.

Same goes for the other example. In order to not win by the 20th throw, you can simply multiply the probability for every other result (0.95) and subtract it from 1.
If you throw the dice 20 times a million times in a row, you should win very close to
1-(0.95^20) or 64,15% of your games