Why do some users have many many answers but no questions of their own? How does that benefit them? Can it prevent suspensions?
Nope. Some people just... don't like writing questions or don't have any to ask.
I write lots of meta questions (and answers) but on my highest reputation site, Movies & TV, I've asked only one compared to 176 answers... and on my second highest reputation site, English Language Learners, I have no questions and 321 answers.
I'm not sure how that's "gaming the system", though... some people are naturally sources of knowledge and others are searchers for knowledge. I'm a native English speaker, so there's not much to ask about on ELL (I have asked a few questions on English Language & Usage, though) but I'm able to answer many questions because of my innate knowledge of the language.
The benefit is the joy of helping others. I love to help people improve their knowledge in the subjects I'm an "expert" in. Sharing my experience with them is a reward... as is the reputation earned for good answers.
We actually incentivize people to write answers by offering more reputation for each upvote received on an answer.
Are there any advantages to not asking questions - nope. But there are no disadvantages, either... well, you can't get some badges if you never ask questions but that's a minor thing.
Suspensions are completely unrelated to writing questions or answers. High reputation users are suspended just like low reputation ones and whether that reputation comes from questions or answers is irrelevant.
Questions feed the site, drive it forward. With no questions, no answers could be written. Answers are what draw users to the site, though. Users who write good answers are valuable but not so valuable as to save them from being suspended.
Depends on why you're here. I have relatively few questions because I tend to use the sites as a way to sharpen my skills and find fun problems to solve over using it primarily as a support mechanism.
So... on point
Why do some users have many many answers but no questions of there own?
Cause that's how they roll, and answering questions is their main interest here. It is a little odd, I suppose, since I sometimes use self answered questions to share knowledge, but say I was a software dev who hung out mainly on the tag of something I wrote, I might not really be inclined to ask questions.
How does that benefit them?
Its fun? I've always felt there's a few classes of legitimate users. We might be here for different things. There's a certain thrill to picking apart and putting together someone elses problem, and presumably some people live for that.
Can it prevent suspensions?
Depends on the reason. You're certainly not going to hit a qban or poor quality question suspension if you post no questions. However, manual suspensions are mostly related to things you've done.
Hypothetically, I could hit enough reputation on one site to get the association bonus, get commenting abilities, and then go cuss out someone in comments to get suspended. Without even posting once!
In answer to the fact based question you asked, Stack Exchange supports a query interface where you could, if you wanted, build and run a query to find users with a high answers:questions ratio.
Take a look at https://data.stackexchange.com/stackoverflow/query/new
You also asked a more subjective "why?" - there's no good provable fact based answer to this.
I suspect most users who seldom ask questions behave that way because they already know enough about a subject that they have no current want or need to know anything else. When that changes, maybe they will ask a question, maybe the will google for an answer.
I answer a lot of SQL questions, yet I don't think I've ever asked one - I know a lot about SQL queries, I've written tens of thousands of them in my life. I even answer sql questions that relate to databases I've never used, or even heard of. Any minor questions I might have during writing an answer, like "how do I escape a column name in SQLite", I hit google for and often I'm led back to stack exchange
To ask my query again on SE without putting some effort into researching its prior existence would be slow, require more typing than hitting google, and likely end up being close voted as a duplicate (because most of what I don't know has already been asked)
There's probably no deep and meaningful conspiracy theory based gaming of the system for high answer:question ratio users; they simply know everything they need/want to
You can delete a bad answer anytime not a question. You have to wait 40 minutes to ask another question anywhere on SE and 3 minutes between answering. That is the advantages I found so far. Feel free to add here.
Precautionary: If you answer too many low-quality answers it will get you suspended faster.