Sometimes $100 a week is too heavy for the regular person and even more so if they live in a country that has lower wages compared to other countries. Moreover, for those who are young and don't have a permanent job, of course they might not be too focused on investing $100 every week in Bitcoin. But time is not a problem in long-term investing because time passes so quickly and the $10 or $20 they invest regularly will not feel they can reach 1 BTC someday.
I think in long term investments we don't have to check price to stabilize our purchases, I mean the price today will be different in the next day. So buying regularly and not caring about the price will give you the perception of accumulating Bitcoin regardless of the current Bitcoin price. We only focus on 0.1 0.2 and so on until we reach 1 BTC in our last stage. 10 years or 20 years is quite a long time if you imagine it, but if we take it easy in investing, of course time will pass very quickly.
Make investment a habit rather then waiting for right time and huge money. Even if you have 10$ spare then start investing with it. Of course we can increase it with time, as with time our earnings are suppose to increased. If you can invest 100$ per week then it's ideal but if you can't invest 100$ per week then invest as much as you have in bitcoin.
There are people who invested small money in Bitcoin and finds that it has increased enormously over a period of time,
Man buys $27 of bitcoin, forgets about them, finds they’re now worth $886k.
There is clear evidence available that price of bitcoin goes up with time. So invest for long term if you want a good return on your investment.