drive sizes have nothing to do with P/E as P/E is specified "per cell" : if you have 100MB SSD or 16TB SSD and it can do 1.000 P/E cycles, it simply only can do 1.000 program/erase cycles. That means 100MB SSD would be able to write 100MB x 1000 = 100.000 MB = 100GB of data (0.1TBW endurance) and 16TB SSD with 1.000 P/E cycles would be able to write 16TB x 1000 = 16000 TB of data = 16000TBW endurance. Yes, the resulting total endurance is extremely different, but the fact that both drives were able to write 1.000 times IN EACH CELL stays intact and this is exactly what P/E is all about.
Bigger drive has more cells so it can write more data, but each cell only can be written 1.000 times, not more. This didn't change with capacity. Capacity == drive size has absolutely nothing to do with P/E cycles "per se".
Just because controllers got better and better, just because they are able to heavily optimize writes and drive down write amplification, just thanks to that SSD didn't collapse yet. If there would be no improvement in controllers, we would be done by now with customer class.
Endurance and lithography process have very very crucial relationship. This is no secret information, this is not just me saying it - you can find it everywhere on internet. Drives have generally gone down in P/E specification with process shrinks despite of advances in every other aspect and you are fully right - controllers have gotten better and better, much better than what they were years ago. If they wouldn't, oooh I don't want to know.
PS: in order to mask reliability drops, manufacturers are becoming more pushed and "more brave over time". In past, when they specified 100.000 P/E cycles, that thing was easily able to handle LET'S SAY 1.000.000 cycles so 10x more. Today, when they specify 5.000 P/E cycles for any lithography, you won't get 50.000 P/E by any chance - you'll be VERY lucky when you get 10.000 P/E, especially in consumer-class. Why is that ? Shrinking profits, less margins, extreme pressure on price everywhere, faster product cycles and need to satisfy shareholders, nobody really is able to tear down consumer-class SSDs is TYPICAL environments today (and those rare few who are, hell we'll cover them with warranty and replace their torn-apart-beaten-to-death SSDs so they don't start screaming on internet... well it's directly Samsung with 850Pro who says 150TBW but they will individually consider case-by-case if somebody crossed it), stuff like that.
Back to what this topic should be about...