Software tie-ratios don't really mean much, if software is selling at a faster rate than hardware, then the software tie-ratios will end up higher, which PS4, Vita and 3DS are all experiencing because they're at the end of their lifecycle. They're all dependant on how fast or slow the hardware is selling.
Sure, the PS4, 3DS and Vita all have similar software tie-ratios but the 3DS has sold double the amount of software and almost double the amount of hardware of PS4 and Vita combined.
(
Last record on gamedatalibrary week ending September 23rd 2018)
PS4
HW: 7.115.682
SW: 33.197.541
tie-ratio: 1:4.7
Vita
HW: 5.931.609
SW: 24.118.811
tie-ratio: 1:4.1
3DS
HW: 24.210.427
SW: 119.233.021
tie-ratio: 1:4.9
Switch
HW: 5.090.333
SW: 13.973.349
tie-ratio: 1:2.7