I got this verbally from my uncle, whose day job was to find ways to extract more oil from rocks.

To begin with, the oil is there, stably, at rest. At some point people come along, estimate the layout of the rocks (many km³ and far underground) and drill holes to change the way the pressure works and make as much as possible of the oil flow to a particular location. The geology decides how much that is, modified by the paths of the holes involved, and also by how much water is pumped in, where.

If you now close it quickly, the pressure's going to change somehow and you don't know precisely where and how. The end effect may be that when you reopen, something has changed down there such that instead of extracting 40% of the total oil you can only get 39%. Or such that you have to drill more holes in order to gain back your production velocity, the cost of which is far higher than producing at a loss for a month.