Had SMS supported group text, Whatsapp would have never existed in the 1st world (and had SMS been free in Asia, Whatsapp would have never existed at all).
When WhatsApp first came out, lots of people (in the West) paid punishingly high costs for sending an SMS at all.
Being able to communicate via [free wifi/a much smaller data cost] was a big selling point.
Yes, I suspect it's a function of average-age-on-HN, but certainly remember when teens would have a phone plan based on how many "free" texts were included.