Probably because most of the time it's not that huge a deal - you don't need many aircraft to dominate vs. the AI (I succeeded with 6 oil from a single well yesterday), and a lot of the (useful, as opposed to tanks) things that should need oil don't (destroyers, battleships, subs).
I certainly wouldn't go so far as the modder who for some reason created a mod specifically designed, so it says, "to make oil useful", when oil is already the most useful strategic resource in the game after aluminium (and considering how much more game-changing bombers are than even rocket artillery, possibly moreso), but when I've played as Arabia the double oil is mostly excess (which, characterfully, you can of course sell to the highest bidder).
More to the point, double oil is already in the UA, so it's not going to change anything in the way the Arabs play, unlike the religious pressure change.
Arabia was powerful before and is probably a superpower now, but mostly I just think this is one of the single most characterful UAs in the game, ticking nearly every box for a civ that has a lot of associated traits (trade, religion, oil). The religious element also ties in with Harun as a leader; the old UA didn't really reflect anything about the specific leader choice, since Harun wasn't known particularly for ruling a trading empire, or for commerce.
I'm much more excited for Arabia's new UA than for France's (or any of the minor tweaks in G&K), and I think it's rather a shame so few civs were changed given the potential this suggests for coming up with innovative and characterful changes to existing civs.