They want the index to be representative of the top stocks listed on the Nasdaq, even if they are brand new. The Nasdaq 100 in particular is a marketing tool for the stock exchange, it's not a particularly principled index.
Quote from Cameron Lilja, Nasdaq's global head of index solutions:
"It is not necessarily representative to have a company that's big and could have a sizable representation in the index to keep them out for that long," Lilja said in an interview. "We're seeing share and corporate structures change - and companies that are staying private considerably longer are thus growing to be truly mega-cap companies before they even come to the public markets."
There's been fewer IPOs recently so Nasdaq and competitors are all racing to woo the few big ones to list with them.
Tens and hundreds of thousands of dollars for listing. But they make money from the trading and associated services they facilitate, hence the desire to have the largest most liquid stocks.
They should just have their own criteria for inclusion in the fund.