I wouldn't think that this is a big deal for most people - if you sit for a whole day and listen to other conversations, you'll find that people aren't that courteous at communicating no-electronically either.
In the specific examples you've highlighted, I would say that not everyone checks their phone all that often, they might be busy when you text them, see it, and then forget to reply, or their phone might be out of charge.
Making plans depends more on how organised people are, rather than specific communication skills. I've had people cancel on me an hour or so before we were meant to meet up - which is both inconsiderate and annoying, but simply because they are un-organised, not unable to communicate.
How old are you? It sounds to me like you're in secondary school/sixth form, and people don't tend to take work seriously at that age, so class-mates probably wont check their e-mails, and if it's about work, won't want to reply/bother to do it.
Overall, I wouldn't call you "over-eager", just better organised than other people. Unfortunately this probably won't change, since there are always people who leave plans to the last minute, but when everyone's older, they will probably reply to you more promptly.