When I watched the DVD commentary for Brazil, I think it was Gilliam who said something like, in the very bureaucratic environment of this office scene, they thought it fitting that the monitors should utilize the least efficient or convenient design. Hence, tiny screens and giant magnifying glasses.
I can imagine, in this fictional universe, conditions could be such that this design is simply the way monitors must be—what if, for instance, in the world of Brazil, some resource constraint makes it such that cathode ray tubes can’t be manufactured beyond a certain size?
At the same time, here Brazil does what a lot of good SF does, which is to remind us that the way things are isn’t by necessity the only way they can be.
The monitor joke of Brazil is that these people are using the least sensible method of doing something when a more sensible method is, to us, patently obvious.
Put differently, it never hurts to step outside ourselves a bit and imagine what are the varied instances in which we are, right now, doing the same thing as the characters in this frame.