I appreciate that people with good/unlimited internet connections don't often care about the size of websites. But it does matter for both the environment and those on limited data plans e.g. my phone has 250MB/month and then have to pay 1p/MB above that.
I monitor UK local authority homepage sizes and, for each, list their biggest resources and give tips on what they could do https://open-innovations.github.io/council-website-emissions/ Usually it is massive images that they could easily optimise.
The largest individual resources on UK council homepages currently are:
1) https://www.newham.gov.uk/images/shutterstock_754478737.jpg a 13.3MB photo of some vapes from Newham Council
2) https://www.northampton.gov.uk/images/AbingtonParkIS_Cropped_1.jpg a 9.1MB photo of a park from Northampton Council
3) https://www.warwickshire.gov.uk/images/MicrosoftTeams_image__5__2.png a 8.6MB photo of some hands from Warwickshire Council
4) https://www.reigate-banstead.gov.uk/images/my_account_reigate_banstead_borough_council_carousel_banner.png a 7.9MB graphic from Reigate & Banstead Council
5) http://www.nottinghamcity.gov.uk/media/3082479/loxley-picture.jpg a 7MB photo of a building from Nottingham City Council
Newham Council's homepage is 16MB in size which means that single photo is 83% of their page load (and would cost me 13p on my phone). It is squashed into a tiny 273x182px box.