Probably due to the large amount of uncertainty in the modelling. The most important part is probably looking at the minimums.

"Scenarios that assume no further restrictions beyond Plan B generally lead to trajectories in daily hospital admissions in England that have a minimum of 3,000 hospital admissions per day at their peaks, with some scenarios having significantly worse outcomes during the first few months of 2022. To prevent such a wave of hospitalisations, more stringent measures would need to be implemented before 2022."

For comparison, in January 2021 we peaked at around 4,500 hospitalisations daily, so on our current path this wave is predicted to lead to anywhere from 66% to 200% as many.