To put it simply, it’s not included because it’s not your money.
When you collect VAT, you’re doing it on behalf of HMRC, and as such it’s a liability or asset, depends on whether you paid it out or have collected it.
It actually shows up on your balance sheet under codes
2201 Purchase Tax Control Account for VAT you’ve paid out (sometimes referred to as “input VAT”), and
2200 Sales Tax Control Account for VAT you’ve collected from sales invoices (sometimes called “output VAT”).
As a VAT registered business, all figures are reported as net figures, which is everything excluding VAT.
I hope that makes sense, and helps!