I wish I could take a peek into the brain of whoever came up with that idea -- ideally, after removing it with a large, sharp rock.
Yeah, right. But it's not just confined to Android apps, for years selecting text with the mouse and copying from within Windows Firefox has been flaky, it can work but often it doesn't. If I want such copy to work for certain then I highlight the text and use Ctrl-c/v to finish the job.
Similarly, selecting some text such as part of a URL is nigh on impossible in Firefox (the URL becomes a single entity). Also, when selecting such text it's better approached starting after the text rather than before and working backwards—and even then it's best to start from a few words further on and discard the extra after the paste. Sometimes, with 'awkward' pages it's best to do a 'Select all' on Android or Ctrl-a elsewhere then paste into a text editor and fine tune one's selection from there.
It's ridiculous. I cannot understand why this hasn't been fixed, surely I'm not the only one who experiences these problems.
On the other hand, it's obvious that given a message like "My address is 123 Xyzzy Rd, come anytime," the user would only want to select a subset, not the entire message.
Right, it saves typing when using some of the words elsewhere, and or when there's something in the bubble like a URL or awkward Unicode character. Copying the text is much quicker than regenerating it from scratch—or it ought to be!
Also, with an address and or phone number it saves making copying errors (I regularly copy text this way).