I'm basically just speculating here. But I do know many people believe in LN. Why else would there already be so many different wallets out there, some with very active development?
Just because someone is developing a product doesn't mean that the product will be successful. All developers believe in their product, and all hope that they will be a great success. But only a few out of hundreds achieve success. 
It took me a couple of days to understand how cool Bitcoin is. But I spent about six months intermittently on LN, but I still didn't understand what the optimism of LN developers is based on. There are too many unavoidable design flaws. My experience and my intuition tell me that LN has ~1% chance of great success.
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Either fools or fans will risk their money for a profit of less than 1% per year.
If fools and fans make LN grow, I'm okay with that The ranks of big-money fools and big-money fans aren't that numerous.Quote
If people use custodial services, they don't need LN.
That's not true. Any exchange, casino or random website can create their own custodial "tipping service". The great thing from making a LN custodial service is that it also works externally. BlueWallet for instance is custodial, if I make a payment to another BlueWallet user, nothing happens on the Lightning Network. But I can use the same wallet to make an external payment too. Without that, there wouldn't be any use for this wallet.[/quote]
The user doesn't need LN. The custodial service needs LN.
If your external recipient also uses a custodial service, then they don't need LN either. And two custodial services can agree among themselves and without any LN. Why would they invest heavily in a particular channel? The way banks work with each other now.