An SSTO could launch, orbit, return, refuel, and re-launch in the same day. For high-value cargo where the mass it not too much (c.f. humans) this might actually make sense.
If you want to deliver cargo or people to a specific orbit and a specific place, say the ISS, you're not gonna be able to turnover a SSTO in a day. Even a week might not be enough for a quick return trip to and from the ISS. All this time your expensive ground to orbit capacity is idle.
A first stage can launch a second stage into orbit and return to launch site in less than 15min. How fast you can turn it around for relaunch is an engineering challenge, but there's no fundamental reason you couldn't do it in a day or even in an hour.
There is another reason for the leisurely approach for manned spacecraft. Studies have shown that something like 75% of spacefarers suffer from Space Acclimatization Sickness, generally lasting 1-3 days before your body gets used to zero-gee and you are fine. A leisurely approach lets an astronaut deal with that phase NOT in the shared space station that spends decades in outer space, but in the capsule which will be coming back down in a few months.
SAS is a major limitation on space tourism, incidentally. You'll notice that there are very few plans between 15 minute suborbital hops and two weeks in space: that's because if even trained, physically fit astronauts take 1-3 days to adapt to space, no one is sure what a person who is not as trained will do, and if the word of mouth is "I went into space for three days and felt sick the entire time" that's not a good customer experience.
Also, YAGNI. Right now, it's not certain that we will ever see a time when trips to space are as commonplace as commercial flights. It's far enough off that, even if we take for the sake of argument that it does eventually happen, there's no particular reason to believe that the vehicles we use to do it will be chemical rockets.
That too. If we get sci-fi grade engines, anything can be SSTO.