That's probably why the line didn't go any further. The isotope analysis does suggest that the very last known spinosaurids didn't spend much time in water, and Spinosaurus in particular just wasn't well-adapted for a terrestrial lifestyle.
I don't expect Carcharodontosaurus would particularly want to get scrappy with Spinosaurus (the latest estimates I've heard are over 10 tonnes for the adults), but even if the spinos were able to scavenge food from other theropods, it'd be very hard for them to subsist on that alone.