A "day," for example, is a measure of real time -- as is a "year." But the notion that a "year" begins and ends at the exact start/finish of a "day" is purely a human construct.
A "month" is loosely based on lunar cycles, but there is nothing that ties months directly to days and years, either.
Exactly. Expecting them all to line up is just pure human conceit.
Now, if you are a Christian, you could try to make an argument from Genesis, about God setting the lights in the heaven for us to measure the times and seasons, and then wonder why they are not aligned more perfectly in order to facilitate that. If you want to make that argument, though, then you already have to accept the proposition of the Biblical God at work, and then you’d also have to accept the proposition that God’s will is not always comprehensible to us, so your argument would be self-defeating.