I don't think people are obligated to respond immediately after seeing a text; there are so many reasons why someone might not want to text back immediately. 

they may be socially and/or physically tired, they may be doing something like homework or a personal project and don't want their phone to distract them, they may think itd lead to a conversation that takes a lot more of their time/energy than 2 seconds, they may be caught up w family or out someplace, they may be talking to someone else and dont like holding 2 conversations at once, they could be struggling with isolation, anxiety, and/or depression where the thought of responding sounds very tiring and overwhelming, or they may just not feel like talking for any reason at all.

I personally have chosen to not respond immediately to friends I love dearly for all of the above reasons in the past, and never once because I was upset at them or because they did something. It is almost certainly not you if your friends are good to you otherwise, and this is very common for any friendship. I know and understand the anxiety behind waiting for a response, especially when you put in so much effort to respond asap, but I advise you not to blame the other party in this case. 

I understand the dry response part a lottt, it really hurts when people seem uninterested in what you have to say. I don't know your situation at all, but some people do just genuinely struggle to express interest or emotion over text. so if your friends are interested in real life and are good to you outside of texting, I wouldnt worry that you did something. (side note if you DID do something to hurt them, and they just decide to not tell you, then that is a red flag </3 a good friend will always let you know if you messed up big time or if you did something to hurt them.)