Where can 373s run to that 374s can't?
South of France, allegedly, but even if they solved that, my logic still stands. It's a fairly arbitrary suggestion that they get rid of a significant portion of their planned long term fleet based on a dip in demand when nobody really knows how soon it will recover. So even if it is not a geographical limitation, a fleet that is too small creates an identical problem.
I am certain that the market will recover; it may take a couple of years. But no competent business would dispense with that chunk of fully owned fully depreciated capital stock (that they expected to need in the medium term) so soon after an unexpected dip in business. They'd have no flexibility to respond to the future market other than to order more 374s, which may take years and cost tens of millions. It'll recover, and if they were left high and dry without enough stock then they'd look pretty silly having recovered little cash from the assets.
People will say the recovery is uncertain, but uncertainty works both ways and contingency is important. The stock being owned not leased is a substantial factor here. Grand Central abandoned their plans for stock they were leasing on an already speculative business case. BA have sold or scrapped their fully depreciated but expensive to operate 747 fleet - but they only had between 0-3 years left already.