How does this mean grandfathered plots are dropping, and I quote you, "every week"? Literally nothing you have said here states how they drop every week. This is just you saying "well they can't sell the personal houses, so why would they keep them?". Just like how you don't know how many grandfathered plots actually do drop in any given space of time, you also do not know the personal reasons why grandfathered players hang on to their plots. At best you can guess.
I see so what you're actually saying is "grandfathered plots become free sometimes". Absolutely nothing here suggests that it would have to be every week. Literally zero.
And what is this "lack of incentive to keep extra personal houses"? I can't even begin to count how many times in this thread I have been told about people who lovingly decorated their 3/7/15/etc houses. Have you suddenly decided that this isn't an incentive just to suit your argument? Have you now decided that pair on Mateus are actually real estate agents instead of people who actually enjoy owning many houses? Well at least you admitted that bragging rights is a possible incentive.