How do you get millions of people to decide to stop going to whichever site they are currently going to and go to your site instead?
If you need proof this (i.e participating for a shot at monetary reward) works, look back at when Valve first implemented the ability to trade cosmetics with TF2, and look at how that evolved.
Its actually simple enough to where Im surprised this hasn't been done already considering this happened https://finematics.com/vampire-attack-sushiswap-explained/
You of course need to design the system to be secure. You can do this in a number of ways.
I wonder how that translates to creating a new Reddit?
Which product manager told you this? How does one measure how much "better" a product is than another? How does one then measure "willingness" to switch?
Nevertheless, if reddit gets "10x worse", isn't that where the opportunity lies?
r/Compilers has about 14,000 members. Again, how will you find that many people willing to contribute on that topic to make it worthwhile?
r/ProgrammingLanguages has about 90,000 members.
You have a chicken and egg problem -- until you have enough actively participating members, there is no benefit to moving.
More realistically though the truth is that mismanagement, changing circumstances and incentives (Reddit shifting from open platform to IPO prep for example), and a lack of innovation to keep up with changing demands all stand as risks to an existing platform. Arguably your job isn't to convince millions to drop their old site, it's to strike when said site does that themselves.
If there had been a working, scaled, viable alternative to Reddit last month... Reddit would no longer exist.