SMS spammers could be tackled with a couple of regexps if the will was there. The fact that these scams still work is a sign to me that there simply is no will to tackle any of this at the telco level. They know exactly what is going on.
There is already keyword filtering. Try using the word "election" in SMS at a certain time of year. A certain US political party complained about this. E2EE is not compatible with content based filtering.
Lots of telcos are doing exactly this, doesn't really work very well. The spammers just switch to more generic messages you can't realistically filter out.