I'm in Trafford. People move to the area because of the schools so usually people who want to use the grammars know about them well in advance. My baby group was full of Altrincham residents talking about how they wanted to send their newborns to the grammars when they grew up!
So I've known about the schools from before I had dc. I thought about it quite hard as I chose a primary for my child because secondary options is one of the questions I asked when viewing the school.
I lined up a tutor well in advance and was prepared to tutor from year 4. As in I got my name down for a tutor when ds was in year 3. I subsequently decided to use a tutor from year 5 but he was tested for ability from year 4 and I spoke to his teachers in years 3 and 4 to check it was a suitable option for him.
Year 4 is when many parents start looking at schools to get a sense of what's out there even if not going to grammars. There's a lot of choice.
The majority of schools viewing goes on in year 5. The grammars open days are May/June time. By the time you start year 6 there's only 2 months to the schools deadline at the end of October.
There's always some parents who aren't bothered, send their kids to the nearest (failing) school and just turn up at the one open day in September of year 6.
You managed to leave it til just before the exam so you found out about the grammar system in August before year 6. That's on you, sorry to sound judgemental.
Trafford is unusual. There's very few places which still operate grammars. A large proportion of the kids have non UK parents so it's not mainly a white middle class enclave.