Emotional manipulation is the obvious answer.

Sunk cost "fallacy" helps the scammer a lot.

They start with a trivial amount and build from there. Each time, it's emotionally harder for the victim to accept the romance they built in their minds does not exist, AND the money they paid was not spent on a good cause.

It's much easier to deceive a person when their subconscious is collaborating with the scammer.

They are good at convincing you that they have some immediate financial need.

Many people on dating apps are so lonely that anyone who can pretend to be interested, friendly can easily manipulate a lonely person into falling for them. Basically, the scammers are using the same techniques that con-men use to fleece their marks.

I got so many bots and romance-scammers that I quit all dating apps years ago.

Having known scam victims here & there since before there was an internet - the short answer is that some people's heads are just wired differently. In a high-enough-trust society, they may be model citizens. But watch 'em interact with a shyster, and you'll understand the old saying about "a sucker born every minute".

Indeed, and why would you send somebody any money, if you haven't met them IRL?

Also, anyone who acts too interested in me would be an instant red flag.