Why are they tuned like this? Unlike the rest of strings
Simply put because there aren't any strings made that can go high enough without breaking.
Could this be achieved with the standard set of unwounded strings?
No. Or at least not without sounding terrible and having intonation problems.
Should I increase one octave of the higher paired string or reduce one octave the lower paired string?
Trying to increase an octave of a string will break the string, the guitar or both. Tuning a string an octave below its pitch will result in it being floppy, quiet, with a muddy tone, and to go completely out of tune at the slightest touch
Even if possible, why would doing this could be unideal or discouraged?
Including a 1 octave up b and e could be cool, it's just not really possible on a guitar with a normal scale length. You could include a low b and a low e, but that would then mean that the E and B strings were essentially an octave below the other strings, the B string would now be lower than the G and D string not higher. It's not wrong per se, but it would make a lot of common chord voicings sound very different (and mostly bad), and make playing the guitar well more difficult: you'd've more or less invented a new tuning where the last 2 strings of the guitar are tuned an octave down. Sorta like the opposite of a ukulele...