Actually there's nothing wrong at buying whenever you have the money available but I think what he/she meant by timing the market is just by buying at each dip that occurs, take for instance a week+ ago bitcoin price moved up to $47,000+ and after a while dropped to $39,000 then later took a leap to around $43/42,000+ right now (as at the time am writing this). For a investor that is timing the market he/she will know that $39k is a right time to buy because the price will surely move up again for him to make profit and for sure it did moved from $39k to $43k, so isn't it a right timer for any investor? We know the market is unpredictable but there are moves that we will critically observe and we won't need a fortuneteller to tell us what could happen next, only experience will tell.
You’re suggestion is not wrong because that’s really an efficient way to accumulate but not all people have a good patience on waiting and the luxury to frequently check the price like me due to the nature of my work.
I usually purchased whenever I’m feeling that price is decreased a little bit while I have spare money that I can use to purchased Bitcoin. Not always I have free money since I have other things to do with my money especially if I’m currently not using it because I can always wait for my salary to get another money that I can dedicate for whatever stuff that I failed to buy before. That’s why I always purchased whenever I feel like I don’t have anything to do with my spare money aside from buying Bitcoin instead of wasting my time waiting for the perfect dump while we all know that Bitcoin price will surely grow astronomically in the future. I’m investing and not trading so I don’t care about minor price difference of my buy if the end goal is still the same.