As with most things, it's a matter of habit.
Things we know are 'easy', things we don't know are 'difficult'.
There's no rocketscience about that.
I started out writing T-SQL the old way, and switched to ANSI style sometime around y2k.
At that time ANSI was hard, difficult, weird, strange, awkward... take your pick.
Of course that was because in the beginning it was something that I didn't knew too well.
But with practice comes perfect, and once you get used to it there are no regrets.
ANSI is way more clear, concise and easy to write and moreover, to read. There's no doubt when
you read a query what the author intended with it when it was written (assuming it was written correctly ofc)
The major point is that there's no ambiguity for outer joins - a quite tricky area to 'get right'.
I should add as a final note a plug for aliasing. Always alias everything. ANSI outer joins with aliases on all columns and tables is pretty much self-documenting code.