Quote: those were the days "There wasnt any major sport events last year or next year it only takes 4 hours for the two semis.'"
They aren't all huge things like the soccer World Cup, but are there every day all day on tv. Wimbledon Championships for example is every year last week in June and first week in July and gets wall to wall coverage. That is where the SF would naturally fall (midway between QF and Final). You may be able to fit the SFs in in the middle of July maybe every two years at best but would be mucking about with the schedule each year giving the impression that it is worthless as it gets shunted out of the way for other stuff. The RFL want regular dates for the SFs and Final.
The BBC doesn't have a sports channel and has to show a range of programming, even though as you say a two hour SF broadcast could be fitted in time wise they can't (or won't) get rid of a non sports programme to saturate the channel with sport.