Problem With Flipping New Domains

Just as there are homes we purchase with the goal of flipping them for a profit, there are websites you'll build to flip as well. In fact, there are some sites you'll want to setup just so you can sell them down the road.
That's what happened to me at least... Just as a real estate flipper would slap on a new coat of paint and
make repairs to the home they want to sell, my sites needed the same kind of TLC to make them more attractive.
...... after the guy I hired had completed renovating the site, which was bought more than 2 years ago, I put it up for sale on a popular website marketplace. Even though the site didn't have much traffic and hadn't made a dime in Adsense or affiliate income over the last 2 years, it still sold for 5 times the amount I paid for it.
Not too bad, right?

After the first flipped site was sold with good profits, I decided to buy, renovate, and flip new domains
instead.
Big mistake!!
Although I didn't know it at the time, the process of buying and flipping newly registered domains is an entirely different animal compared to flipping established sites.

After a few weeks flipping new domains, and only seeing less than half the returns I enjoyed earlier, I got confused and tries to figure out with the hired guy what was happening.
As you can imagine, we'd developed a pretty effective system for renovating and selling these sites... so the formula was already battle tested.... they should be sold quickly, with multiple bidders fighting for it but not otherwise. What's happening??