I think you are being very generous to SQ, by using a very limited concept of "affected". I'd say a very large number (the majority) of people are affected by hard expiry. If one set of points has a hard expiry, then you are inevitably forced to use them at a non-optimal time, at least occasionally. If I can get an AC award that's better value than SQ, but the SQ points are going to expire, then I am forced to use SQ, despite them not being the best choice. That consequently means not using AC at their optimal value either.
There's also a flow-on effect for earning, as well as redeeming. Because of the hard expiry, if there is only one good-value SQ award on the horizon, you may be forced to put more earnings towards SQ (e.g. by transferring) in order to have sufficient balance for that award. This is exactly what happened to me. I transferred some Marriott points over to SQ to have enough to get a really good value award. I transferred the exact number, so that my SQ account went to zero and have never used them again, because they are just too much of a pain in the cough to manage.
Avoiding hard expiry means necessarily earning a ton or plundering transfer options (which may not be ideal) and then using them frequently, even when there is better value in other schemes (e.g. AC and AA) on some routes.
(If someone offered me 500k in my choice of the listed programs, I'd take SQ over QF, but that is a totally different situation to earning them from scratch.)