I don’t think it is happening as much as you say so. I am not doing explo anymore but I spent 2 months in null sec doing relic and every data except superior sleeper as well.
And no it is not happening unless it is specific to a region.
You are overexaggerating either willingly or maybe even unwillingly. Unwillingly because peoples tent to focus and remember the bad things more than the good. So you will remember the times when you found carbon or nothing, especially because that situation is connected to an emotion “■■■■ again nothing”, but you will not remember the times when you found okay loot or good loot.
I also hate the fact that sites containst carbon, nothing or and this is what I saw the first time this year a metal scrap in them. In my opinion it would be far better if the total loot value of the site was appropriatelly distributed between cans - it would also reduced the urge to cherry pick. But it is as it is and CCP won’t do ■■■■ about it I am pretty sure about. And at least relic sites are providing a really good total loot value (on average) and you can make some really decent ISK doing explo in null.
Data sites on the other hand… Except covert and sleeper sites they are waste of time and you would do better to ignore them to maximize your profit… That is the main issue that needs solving in exploration imo.
Anyway, if you disagree and want to keep claiming the loot tables are broken, you should keep track of the loot and write it down for a whole month. This is just your memory screwing you. Btw, how much did you earn by explo in that month?