I haven't done a knk in years, and don't really miss it, apart from the fact the only tools I needed for KnK were a fermenter, spoon and can opener, and I could make a beer whenever I want!. AG is a different ballgame.
The three major factors are Time, space, expense.
Sydney alone is getting pretty bloody crowded, and I can only guess that a lot of new brewers are living in units, with limited space, and neighbours who'll complain about the delicious smell of boiling wort wafting across the many balconies.
SPACE: The amount of brewing gear that's in my shed is getting a bit ridiculous. Eg, Urn, mash tun, fermenters, Then there's the grain tubs and extra storage tubs with random brewing gear, Not to mention the odd crap round the side of the house that comes out on brewdays.
And in a "WTF have I done" move, I recently purchased a grain mill off a mate, and have to make up a hopper now. argh, more gear!
TIME: A kit n kilo. an hour at the most. Done.
AG = Speaking for myself, It takes me weeks to plan a brewday. Finding a good day to brew, and planning around it, getting the recipe sorted, ingredients bought & grain milled. I actually do my boiling at night, cos I just don't feel safe with a 3 ring burner and 40L of boiling liquid with my kids around.
Expense = gear costs money, but yeah AG means I can cheaply make beers I like that would normally cost $80+ per slab. I love belgians (who doesn't!)
Like any hobby, you can tend to get a bit obsessed, acquiring gear along the way. I think I've got to a point where I'm now streamlining what I actually need.
Bit of a ramble, but I hope this helps.