I've found that in the first guild heists and dungeons there are new players who have party chat settings broken and as soon as I repeat it in 'Say' mode they stop and then we're able to communicate, fix their settings to turn party chat on, and they're good to go. Why would they disable it? Oh, for the same reason as so many new players do, they go level 1-15 getting RMT tells and not knowing what to do about them and they turn off just about everything and screw up their log settings. The two level 10 guild heists can be completed without realizing there's communication going on, because even if people don't read the box (which they should) they can finish them doing them the wrong way (and since they're there to teach mechanics for upcoming instances doing them the right way matters.

The following happened the other day it was actually really cute I was helping out a New Adventurer in Gridania who had a question for me and didn't get my Tell back and we figured out they had Say on but Tell off (blame RMT and those who allow it to run rampant). They said 'My shouts don't work either or no one responds.' and I asked how so and they said here's an example which was something like- "HEY I NEED HELP AGAINST THESE THREE VENEMOUS TOADSTOOLS!'. So then I said- 'That's not actually using Shout, that's just using all caps in Say mode.'

Some people of course aren't receptive to advice and I won't waste my time arguing with someone over something that's supposed to make the experience better for them, but the in general the following holds true- Help a new player out, and they'll never forget you for it. Treat a new player really horribly, and they'll never forget you for it.