A lot of people have the idea that you can write a first draft and then go back and tidy it up a bit for your second draft. And there are writers like that, but for a lot, maybe the majority, especially for your first few books while you are learning to write a long form project, your first draft is a collection of ideas. You're telling the story to yourself - after that, you have to go back and make it good enough to be read by others. I doubt there is one word of my first draft in the draft I'm currently querying with.
If it helps, this is roughly what each draft I worked on achieved:
My first draft was the basics of getting the story out. But I also learned that I had too many pov characters and needed to drop from 5 to 3. I also learned that an ambitious, unusual, idea I had was doable - even if it was a bit on the nose in the first draft.
My second draft was structural. By dropping two pov characters, I had to figure out which chapters would go to the remaining pov characters, and which were right/wrong from those three originally. I also had an argument that happened over and over in the first draft (realistic in real life - dull in a book), so I needed to find a way to realistically seed and interrupt the conflict. Then make it bigger once it happened.
My third draft, I actually called draft 3, 4 and 5, as that draft was where I polished up each chapter and made the writing good. Not one chapter took less than two rewrites - usually I'd write it one day, then redo it the next day. With lots of going over and back on those two writes. Some chapters were insanely sticky - with a couple of them taking the best part of two weeks to get right. Usually a sign that I was making them far too convoluted and/or starting at the wrong moment. - So those chapters had 11-12 drafts. And through this section of drafting, I was still coming up with ideas
My sixth draft was intended as a polishing draft, as I thought I was in a really good state at that point. I knew my writing had improved through the book, so anticipated that the earlier chapters would need real fine tuning, but it turned out, that even with all the drafting, sections of the book, even towards the end, were unnecessarily baggy. And a few chapters, usually the ones I'd really struggled with - were too sparse and needed writing up a little. I dropped from >103k words to <95k in that draft. I also realised that flashback chapters, I had written were inserted unevenly into the main text, so I rejigged those.
Draft seven, became the polishing draft. Lots of small changes, grammar mistakes fixed, I went through all my 'its' and 'it's,' double checked that I had consistent spelling of names that can be spelled more than one way (I didn't), and any names that I'd changed between drafts.
I also realised at this point that I had an issue I nearly missed. I write really close third person, so one of the important secondary characters is only ever named in the chapters from the pov of one characters. So, for example, in the other chapters she is always 'Mum' or 'her mother,' or 'Gran' or her 'her grandmother.' It isn't until 40% of the way through the book that this character is in a scene with the third pov character, and that character thinks of her as 'Sarah Mulligan' or 'Sarah.' It's the very first time a reader would come across her name and they'd almost certainly be wondering who the fuck this Sarah woman is, and why is she in the middle of this tense family conflict. So I had to go back and find natural ways to include her name and position as Mum/Gran, which was quite difficult.
And if I get an agent, I assume I'll have to do a certain amount of re-writing. If I get a publishing deal, I assume there will be more.
All of this is to say, that it's an absolute tonne of work after draft one. Completing a full first draft is an amazing achievement. But it's a bit like completing couch to 5k. A serious achievement that puts you ahead of most people. But getting the whole novel to a really good state is like managing a full marathon.