I don't see why they feel the need to ban babies in an empty coffee place because they want to fill it with business lunches later on in the day, but I suppose thats up to them.
Because they are a hotel. Their main business is selling rooms and having guests. These are mainly going to be for business people with the odd tourist in Surbiton. Often these type of guests are regular returners too.
If their guests are coming to stay and finding that they can't do the work they need to, can't have a working lunch or hold a meeting or sit and work on their laptop because there's a squad of bawling babies and the place is an assault course of prams they are not going to return.
They are a business, not a community centre. They are under no obligation to make their facilities unsuitable for guests paying a minimum of £85 a night for a room for a group who are spending £4 each on a coffee. They would go to the wall in a couple of months.
I would suggest that if the NCT are that desperate to use that venue they pay to use one of their conferencing rooms like the business customers would for groups that size. They won't though, because they want to spend the minimum of cash. Which is why they've made the business decision to prioritise the customers who actually make them money. Because they are, you know, a business.
It looks like even at the weekend their main business has an adult based clubbing focus so not even very suitable for families then. I certainly wouldn't want to nurse my hangover next to an NCT group. And again, that group of customers, weekend clubbers, are going to bring in an awful lot more money than a group of mums drinking coffee.
They're under no obligation to hurt their business to facilitate customers who would drive them into big losses.