The real reason you notice a difference is that in the last couple of years Godaddy has bought up almost all of the domain aftermarket sites, including Dan.com, Bodis, DomainAgents, and they already owned Afternic, Above, and others. The only real competitor to Godaddy's near monopoly is Sedo which is still a great company.
Without sugar coating it, Godaddy's systems are terrible, things like not having SSL, broken landing pages, listing errors, general clunky infrastructure, very slow support, not friendly to cheaper domains in terms of their standard sales flow, and so you have this one main dominating company that has the worst sales flow and support typically, and they then retrofit and change the internals of sites like Dan etc and actually degrade what was working there many times. So the bigger the monopoly continues to get, the worse sales will be because they have less and less incentive to provide a quality service, when the monopoly catches enough business to sustain itself without much effort.
If that wasn't enough, if you are lucky like me and have one of their own ad providers send a visitor to your landing page and decide to ban you for it even though it was their advertising system, they will quietly ban you from things like getting landing revenue and will not tell you that has been done either, they will keep letting your traffic in but will also simply stop paying you. Domain listings also might not syndicate, etc., if you are put on the "bad" list even due to no fault of your own. Then as a domainer, you get to spend years trying to figure out what is wrong and waste thousansd of dollars only to have them eventually tell you years later that oh yeah we banned you at nearly every company that exists to sell domains at, sorry.