Simply put, ease, and efficiency on my end. If I have too many IM services, then I am stuck juggling things around. Which service does this person use is a big issue. With that in mind, I use the minimum number of services, and don’t see value in using other services. For example, I don’t have Telegram, and therefore will not see me installing Telegram. The same will go with many other IM services despite on how popular they are globally.
As of now, I have an iPhone. This phone uses the same application for all of my supported IM services I use. This will include iMessage, RCS, and SMS. In the US, most people will use SMS, and I understand this is not the norm for most people outside of the US, but I was getting too much trash on my Signal, Telegram, and WhatsApp. Since I had no communication with anyone on Signal, nor Telegram, I just cancelled those service. I had 2 people on my WhatsApp. I notified both of those people of me dropping WhatsApp, and provided iMessage, RCS, and SMS as options for them to reach out to.