I married in church and only needed a few months notice BUT the venue wasn't open to all (military church) and we were very flexible with dates.
However, I later worked in the wedding industry and know from friends and family that have married in the last few years that it's far harder now.
Of course it depends on the type of venue and how flexible you are with dates. But it's not just the main venue, it's all the other vendors too get booked up very quickly if they're any good.
So it's the co-ordination factor.
Caterers, celebrant, florist, entertainment, photographer...
Then there's clothes, wedding and bridesmaid dresses in particular. Unless you're willing to wear "off the peg" (which severely limits choices in both style and colour) it takes around 6 months from order date to the dresses being ready, depending also of course on how many bridesmaids and if they're easy to get together for looking and fitting.
Plus of course there are peak wedding seasons, mainly summer but also Easter and Christmas.
Lots to consider.
It's why most couples allow 2-3 years now.
It IS possible to do within a few months but you would need to be really flexible on dates, venue and quality of vendors.