Why can't you highlight text in certain apps?

[TomTomHatesCats]

For example, in an Apple app, like the Messages app, you can copy an entire message, but you can't highlight individual words.

For a non-Apple app example, the Facebook app doesn't let you copy or highlight a post at all. It does let you copy an entire comment responding to a post, but again, won't let you highlight individual words.

What gives?

I'm on an iPhone 6 running iOS 8.1.2.

 

[dustrho]

With Facebook I think it's always been that way. Not sure about other apps but I have seen this behavior before.

 

[C DM]

Different apps decide how they want to implement that.