My experience :

I bought a number of smaller projects that serve as traffic generators to bigger projects, typical freemium services that provide me regular signups on a daily basis.You can make the calc: pay a few thousands for years of free referrals.

I bought a bigger project 10K+ and that has technical issues that need to be resolved (will migrate from Node.js to PHP) but i have an existing customer base that helps understand the problem you try to fix. I am rebuilding the solution but in the same time i can experiment with pricing and traffic generation on the service i bought.. it is a de-risking strategy.

The reason why people sold in general because they don't have the marketing budgets to carry the project when its initial launch spike runs out.

EDIT : I typically pay 5x recurring revenu max or max 1K to 2K for non revenue generating sites that have interesting traffic of an audience I target Edit 2: I want to build a recurring revenue stream to supplement my consulting business