This is the whole point:
When you’re expanding rapidly and want to grow market share above all. Growing that market share with customer acquisition is economically an investment in the future revenue of the business. Advertising is one example of how this might be done.
You can classify investing in your business through advertising spend as an operating expenditure for accounting purposes. And potentially for tax purposes as well.
Now your large positive cashflow does not generate an accounting profit. Because you spent it on something that won’t be capitalised on the balance sheet.
There it is, the answer to OP’s question.
Note you can’t do that buying property plant and equipment (but some structured finance and leasing people might like a word - airlines don’t own their aircraft.)
Perhaps you can think of some examples where you’ve seen huge, massively cash-flow positive businesses in our field that weren’t generating accounting profit. Facebook, Amazon, ..?
The only other way you could sustain repeated loss ina new, growing business is capital raising.
Someone else on the thread mentioned Aswarth Damodoran’s “Free cash flow to equity” IMHO it’s worthwhile avoiding jargon when explaining things simply and concisely.