What u/dikai was getting at was this

Imagine your country relies on products A, B, C, D, etc...

If you sanction A, well now the country needs to switch to B to keep things going smoothly. After a while, when your country has swapped over to B completely, you sanction B. Now that hurts more, and your country needs to scramble harder to fix that problem, so they switch to C, etc...

This is not a perfect analogy, but it explains one of the reasons that sanctions applied over time can hurt more than all the sanctions applied at once.

Also another reason for escalating sanctions as opposed to dropped every sanction known to man at once is to keep some leverage. If you sanction the shit out of Russia with everything all at once, well there is not reason for Russia to listen to you at all since you threw everything at it. But if you do it over time, it leaves you with negotiating power. Even if Putin does not care, many oligarchs may get increasingly nervous with increasing sanctions that hurt them more and more, and that will cause instability.