[cheekyangus]

There's not really a number limit on the video streams, it just depends on what quality is deemed acceptable to the buyers. They could fill it with 100s of thumbnail video streams if they wanted to.

And the non-PSB multiplexes are all carrying a mixture of other services, they aren't carrying identical loads.

COM4 has 3 radio stations, 5 IP services & 2 "teletext" dating services.
COM5 has 5 radio stations.
COM6 has 9 radio stations.

It can't be assumed there's going to be 18 on each when they are differently loaded up currently.

Different content requires different space, you can get away with lower space usage for shopping channels and rolling news as their content is often static or slow moving imagery. They have to balance the multiplexes and mix channel types of different types of content. Remember the problems when all the BBC channels had the same content simultaneously when they were all transmitting the same coverage of Prince Philip's death. They had to shut a few channel services down because the channels had the same data transmission peaks and it affected the entire multiplex.

Freesports needs more space because of the content it shows if it's going to be watchable, the other SD services on the soon-to-close COM7 don't really need as much.