What an interesting process.... No questions about flight numbers etc., but emergency contacts and employment details.
Well, it's fairly understandable
what CBP WANTS to know in advance, is if you are likely to illegaly immigrate to the US, therefore they ask if you have a job and employer back home, which makes you less likely to stay in the US
what they also want to make sure of, is that, in case of an emergency, there is someone in the UK they can contact, in order to take care of you.
What CBP wants to make sure of, before allowing you to come to the US, is that you are not likely to become a burden for the country.
those information will be available to the US immigration officer who will assess if you are allowed to enter the country or not, once you're at the airport (ESTA is just an authorization to board a plane, not to enter the US)
they don't care how and when you enter the USA (flights), they'll know soon enough since you have to go through immigration anyway, and they'll also know through the Advance Passenger Information (API) which is transmitted to CBP even before you board the plane. so they know what plane you're on, even before you leave the tarmac.