It is not “an insane salary”.
The average full time UK salary per the ONS was £39,039 in April 2025 (it will be more by now). A couple each earning this would receive £2,636 each per month after tax so £5,272 net pay. With two children they’d also receive £2,252 of child benefit per year so the equivalent of another £188 per calendar month taking their total net income to £5,460.
A lone parent earning £100,000 will receive net pay of £5,713 due to the incredibly high tax rates on higher earners. They get no child benefit. Their net pay only exceeds that of the couple on average UK salaries by £253 per month: hardly riches.
Given that a nursery place for a single child can often cost more than £2000 per month they will be very significantly poorer than the couple who receive nursery funding. They will also likely need far more childcare because they do not have two parents to split work and childcare between and are likely to be working long hours to earn their high salary. They are also more likely to live in an expensive part of the country to access such a job and to have higher commuting costs.
If the lone parent has two children in childcare they will have only £1,713 per month left to pay their mortgage/ rent, Council tax, bills, food, commuting and for all of the children’s needs like clothes etc.