Especially since there will always be another group of investors that are currently on Step 1.

If Reddit's experience starts sucking once they try to monetize, there will be no shortage of people who are going to offer a superior (i.e. non-monetized) experience with the intent of somehow monetizing The Right Way in the future. Wash, rinse, repeat.

Especially since it's more like

Step 1: Get a lot of users

Step 2: Major losses

Step 3: ?????

Step 4: Profit?

Because actual money making things are very hard to come by? They typically involve either huge amounts of unforseeable luck, or a time machine to go back to before some monopoly was achieved. Or they're borderline illegal, which takes a long time to achieve too because you need to grow the capacity to pay off the politicians. By contrast "look, tons of eyeballs" is much easier to find and hype.

Because it worked well for Google and Facebook