Also, everyone can't be on the same level financially, that's what some people don't understand, cause someone started with a $100 doesn't mean you must start with same amount whereas your discretionary doesn't permit you to, I guess that's another reason why some people keep waiting, Bitcoin investment is done according to one's discretionary and if yours can't allow you invest $100 weekly then starting with $20 or a little more is not a bad idea, it's better than waiting to get $100 before starting.
You have a good point, and also the truth is that we have different financial problems, and not everyone can afford to invest $100 weekly like other investors. That is why it not advisable to wait before we have huge amount of money before we invest. in my opinion, it is better to start with what you can afford without affecting our other needs. Even if it's only $10, $20, or $30, starting with something small is more better than doing nothing and waiting for a right price to buy.
However, investing in Bitcoin, needs patience and efforts. Small investment today can also turn into something big over time. Instead of comparing yourself to people with more discretionary income, focus on what you have today and improve gradually. At least you started somewhere, which is better than sitting in one place and wait for the right time to invest.