Or is it a social distancing measure?
I work in a professional orchestra. We have not had any social distancing on stage since September. It is perfectly safe to be in a crammed pit/on a crammed stage even with Covid, when appropriate measures are taken. We have had 0 transmission since we went back to playing like this, and it’s almost 100 of us on stage, for 5 days each week, and we wear no masks once on stage.
I’m not in the UK but in mainland Europe, so it’s not like in NZ where this would seem normal. Cases here are high, we’re in a third wave now, but playing without social distancing is safe. After dozens of studies and ££££ spent on new ventilation systems and PCR-testing everyone in the building every 48h.
So it’s nothing to do with Covid, it’s to do with money. Reducing the number of musicians who go on tour has always been normal, as the company needs to adapt to the size of smaller regional theatres.
But cutting down on the number of musicians who would perform the original runs in the West End, is just disgraceful. This will leave many people without their main source of income. This will leave the audience without the real experience of watching a show. Substituting not common, more expensive to employ instruments with a keyboard is already way too popular. These shows and their runners make tonnes of money from high ticket prices and relatively low maintenance costs. There is no reason why they shouldn’t employ the original cast and band required for each show.