There's a good chance that, as they deal with multiple freelancers, that there is at least one that has failed to keep to timescales more than once - or covered it up/capitalised on a deadline only being verbal rather than on email. But they've needed to keep them for some reason, such as specialist skills they haven't been able to replace so far.
As a result, rather than risk the more unreliable one taking exception and disappearing/whatever, they're sending everybody the same pointed emails so that Mr or Ms Flaky knows exactly what's required and that they expect to know if there's a problem long before it all goes tits up at the last minute.
I often spend my working day trying to get essential information out of people so I can get the important things done. If I don't remind them when I need something by at least twice beforehand, I know from experience that it won't come until afterwards. I have scraped in literally at the very last second thanks to this happening before, but unlike other colleagues who feel as though they might die of embarassment if they say 'No, you haven't given me enough time for this', I will say well in advance when I need something by (reducing the timescale to allow for their tardiness), remind them just before and on the day itself. And when they still drop stuff in stupidly short timescales, I do say 'This came too late to be able to....'. Which has no repercussions for me, as I have a paper trail showing when I said I'd need something by, plus polite reminders making it very clear at a glance what the deadlines were.
TL;dr Just because you're reliable, that doesn't mean that the others are. And to blindly trust everybody to be as reliable as you would be something they would be very strongly criticised for - and their lack of reminders and chasing would be taken as proof of their incompetence.