Isn't it the way the threshold is calculated rather than the threshold itself which is the problem?
A single earner family loses their entitlement at £100k whereas a dual earner family earning just under £200k, assuming neither partner earns more than £100k, is fine.
At £100k, you start to lose your personal allowance. I'm dreadful at maths, but if you're also losing your childcare entitlement, then what this essentially means is that there is a "black hole" where you are worse off, not better off, if your earn between £100k and around £150k.
Many people are changing their behaviour to avoid this by paying more into their pensions, working less hours or cutting their responsibilities at work. This reduces the overall tax paid and disincentivises parents from progressing at work. It's absolutely crazy!
And as people have pointed out, a single £100k earner could find that their salary didn't cover childcare for 2 kids and a mortgage on a reasonable size home.
It's difficult to believe that if someone had said, "I know what, let's design a really terrible system of funding childcare", that they could have come up with something more illogical than this.