That would be because the pattern on the first password are correctly spelled words and the way passwords are cracked offline (when there's a leak of data being sold somewhere) is that they use dictionary attacks.

This means that a big file containing all known words, and can also include known used passwords from past leaks, is used to try a lot of combinations. A combination of good words that appear 1:1 in these word lists will score way lower in terms of difficulty for a computer to crack. A simple script can add spaces and periods (like your example) between words and they WOULD get your password. By adding only one random character that doesn't fit a pattern (just like your second 't'), you basically force the cracker to try all possible combinations of all characters for the length of your password, which is WAY more difficult.

TLDR: There are more combinations of aaaaaaa, aaaaaab, aaaaaac then there are of matching words together for the same length of password (one.one, one.two, one.three)