Low probability can be reasonable taken as zero.
If it is low enough I think it is reasonable to treat it, when trying to pick a most reasonable decision, as zero.
The poster has the quote wrong. I'm pretty sure it involves an "infinite" number of monkeys. In that case the psalm would emerge in a very short time.
However, the number of monkeys, if not infinite, becomes an issue. To generate a
pre-selected string of enough length in a time less than the age of the universe the number of monkeys might be large beyond a resonable level.
However, the analogy is bad, as I pointed out above, because it leaves out the rachet AND because it supposes a pre-selected very specific string of characters. The probability changes if any of the psalms are acceptable, or any english text of about that length or any text of about that length in any language. They change a lot. And if we were watching out millions of monks we would be just as astonished if any of these things came out.
None of the living organisms that live or have lived are pre-selected in any way. There are umpty-dumpty bejillion others that would be possible outcomes and different from any that did appear.
The odds calculations are silly.