Well, I remember from "Hope & Fear" that the reason, at the time, that Voyager couldn't continue using Arturis' slipstream technology was that it put an extreme amount of pressure on Voyager's structural integrity and just catching up to the Dauntless and getting away almost tore the ship apart.
Of course we saw other improvements that allowed Voyager to occasionally access slip-stream speeds, since "Timeless", even though they didn't make the entire jump, they were able to get further, before future-Kim deactivated the device before the waves slipstream waves overloaded the drive and drove the ship into the ice planet.
And then, of course in "Dark Frontier" Voyager used stolen Borg technology to access slip-stream. But I think there was dialog that mentioned that on Borg ships the drive only works for a finite time before it needs to be replaced. So, when Voyager had the drive, it had already been used by the Borg, plus Voyager had had to use the drive to rescue Seven.