Depends what the message was. Maybe it bored them. Maybe they just don't feel in a talkative mood. I ignore my friends messages, and can do that for days, if I feel down. But I make sure not to read them, so that it won't say that I have. It really annoys me that messages show when someone has seen them.
"Still thinking" is pretty common for me. A lengthy, thoughtful message deserves a lengthy, thoughtful response, and if I'm checking in while eating a burrito with ten minutes of free time I can't write one.
As a chronic slow returner of messages, I agree with all the reasons listed and must add that:
1. It's never a sign that I do not care for a person. I don't feel like I'm abandoning anyone and I don't knowingly inflict sadness because I am not aware of the sadness (until recently one of my friends took forever responding to me. Then I realized).
2. When I forget to respond because life gets in the way, it's not because I care more about life than I can about my friends. It's because life is always in my face.
3. Sometimes I take a while to respond because I am afraid of seeming overeager. It's a weird insecurity thing.
I mean, personally, I can take anywhere from a split second to a couple days to reply. If I'm greeted with a huge wall of text, I'm less inclined to sift through it and pick out the bits I can respond to.
On the other hand, I'm not one for small talk unless I'm genuinely interested in how the other person is or what they've been doing, so a mere 'hi how r u' isn't exactly going to stimulate conversation with me.
If it's a topic I'm not interested in or don't know much about, then I'm also less likely to reply with haste (or at all, really. If you start talking politics to me I will probably blank you).
Then there's the days where my depression shines through and if someone-else starts talking about their problems, I'm really just not in the mood for it. Too much going on in my own head.
It doesn't mean I don't care or don't want to help, I just can't at that moment.
Granted though, even if I'm upset or in a mood, if a close friend seems to really need someone to talk to then I'll force a smile and try to make them feel better.
1. The conversation is starting to go no where.
3. I'm too anxious to deal with the person, or too depressed. I guess sometimes both at once.
4. I'm too busy to be on my phone.
I guess I'm biased with texting. I never really cared much to text anyone, maybe it's because no one interesting cares to speak to me. Because it's just bland conversations I typically just text if I have a question or something and it's really important and I can't call. Texting to me is like a voicemail through writing. You get the message but you don't necessarily have to respond back.
If 2 days bothers you I would drive you to homocide.
If it's deliberate then biggest thing for me is E9 stubbornness stuff, responding to another's requests can feel like obligation and pressure, or it's a need to withdraw. However it's not often deliberate as I have a relatively short attention span and a shit memory so you'll typically either get a response straight away, or it could take a month.
TBH I rarely read texts as soon as they come through. Just checked my phone and there are 13 unread texts, the oldest is 2 weeks old... oops. I just forget, and I hate phones. I get Dory.