They really haven't–Apple has slowly gained on, then outpaced them over the last several years. Apple's chips these days "lap" others, where the best that competitors have to offer perform poorer than last year's design.
The 888 (the first qualcomm chip on the same 5nm process) has approximately equivalent performance (91%) to the Apple A14 in multicore benchmarks, and 71% of the single-thread geekbench 5 score. source: https://www.anandtech.com/show/16325/qualcomm-discloses-snap...
If you look a few years ago, a similar comparison would be the snapdragon 820 vs. Apples A9 (both on samsung's 14nm process, though apple was dual sourcing with TSMC 16nm). Then, the iphone 6s plus scored 535, and the oneplus 3 (using the 820) scores 306 - i.e. 57% of apples performance. On multicore it achieved 77% of the performance (also a larger difference than today).
Qualcomm has been catching up lately on single-thread and multithread perf, just not very quickly (i mean at this rate it'll be well over a decade before they're equal in single thread perf...).
