You are absolutely correct, it is not impossible for someone to invest in Bitcoin without a source of income I mean what they fuck are they using to accumulate if they don't have source of income.
Having a source of income and having a discretionary income are two different things you need to take not off, they are not the same, what is needed to invest in Bitcoin is a discretionary income not a source of income, because their are so many folks that have a source of income but still can't figure out their discretionary income, so if you have a source of income their no guarantee that such person will invest in Bitcoin and be successful if he can't sorts out his discretionary income from there.
Having a source of income is very important in taking care of yourself and your basic needs, but if you can't figure out your discretionary income and you went ahead and invest, you are just gambling, and the end product of such actions wouldn't be pleasing because selling it prematurely will be inevitable.
You need money to be able to invest, a source of income breeds discretionary income, so while a source of income does play a crucial role in generating discretionary income, you don't need a steady source of income, the periodicity and regularity of your income doesn't have to be steady, it just has to be enough for you to be able to get a discretionary income from it after taking care of yourself and your essentials.
So you need discretionary income to invest and you need a means to renew you discretionary income if you want your investment to be consistent but not a steady source of income.
If you have a steady income, it is easier to invest in a more organized and regular manner, because then a certain part of your income can be set aside every month and held for a long time through DCA. But even if you do not have a steady income, if you want to invest in Bitcoin, you can invest as you see fit. For example: A seasonal businessman may not have income for 2-3 months of the year, but he makes good money during the season.
From there, you can easily invest with the remaining money, excluding personal and family expenses, even though he does not earn a regular income and this is discretionary income.
I think that monthly salary or steady income is not necessary for investment, but long-term investment is the most important because it reduces market risk a lot, the profit is not only on the principal amount, but also on the previous profit. It reduces mental stress and helps in achieving financial independence. So first meet the necessary expenses of yourself/your family, then make long-term investment with what you save. And this is the right decision for investment.