When board members resign

You should ask them, even if you don't think they re as good as you'd like. Whatever that means. Some find there's more to the position than they thought or were lead to believe.
Some are one issue board members and as soon as the issue is resolved, they lose interest some burn out because no one else offered to help. And a few may seem to be good, but in fact are rotten to the core and are about to be found out, so they're leaving while they can

Of, course life happens. Your job and family become more demanding, your health or the health of a loved one takes a turn and that must be addressed, so it's to be expected that some things should take priority over the association, so you have no choice but to accept the resignation.

Ideally board member should groom other homeowners who may be willing to take over so the board isn't left in the lurch and the association will continue to function effectively.
Unfortunately that's not always possible, especially if there are other board members who want things their way and drive the good ones away. Finally there's homeowner apathy - they don't care who's on the board or if there a quorum as long as nothing happens that rocks their piece of the world.

I think Cathy said it in a previous post - perhaps the current system of volunteer HOA board's isn't sustainable because the work can be difficult and lives already one damned problem after another. Who wants to come home and then sit around for another two or three hours agonizing over budgets, contractors and whiney neighbors?

In CA per Corporation Codes, don't know about NY, the Board may not "accept" resignations. The resignation is complete on the date the person resigning specifies in writing.

We've had several over the years dn almost always, the person's life has changed so they must resign. In a dozen years only two resigned "in a huff," and one was no good at all.