Polymerization also increases mouthfeel. Bigger molecules typically equal bigger texture(this is why mannoproteins are so important). But this also explains why many ageworthy wines will go in and out of phase(shut down, then open, then back to closed, and back to open).
When I picked up a set of older Willamette Valley wines from the Herbfarm cellar sale, I purchased a number of 2001 Pinot Noirs. 2001 was an understed vintage, that was a bit more old world than the more heralded 1998, 1999, and 2002 vintages. But while seeming a little flat from 2004-2006, they really were brilliant from 2007-2010. I only had a smattering of bottles from 2010-recently, but of the four of the 2001 bottles we have tried from the lot I bought, only one bottle (2001 Hamacher) has been “open”. The other three showed zero inclination to being tired or over the hill. Rather they showed the sort of wound up state that I usually think of shut down wines. I have a few more and am just going to wait 2-3 more years for them. Especially since the 1990s wines we purchased have been mostly excellent to superlative.