I've always wondered why the CGI in these films always look ten times worse when being watched on a home television/monitor.

It's color correction. All Marvel movies have a "house style" that requires some pretty severe color correction and matching during post-production. Movie theater projectors are professionally calibrated and have really high contrast ratios, so the flattening of the coloration is much less pronounced. When shown on a typically calibrated TV with much lower contrast, all the colors get even more flattened and the artificiality of the CGI becomes really apparent.