It was unclear and mostly wrong and showed a lack of expertise
Note that all of this, more or less, was brought up as suggestions for improvement in the comments under your answer (by multiple people including myself). In general, if you are wondering why you are getting downvoted and there are comments pointing out flaws in your answer, they are often related and addressing them is generally to your benefit.
I specifically left my comment, waited a bit to see if you had fixed it, and then downvoted it. My reasons are elaborated below.
It wasn't clear
You talk about a lot of stuff in your answer, a small part of which was correct but all of which was not clear. The context of this question was a new user who clearly has no idea how to play the game so extra clarity is necessary for a great answer. You don't define or reference any of your terms or tell OP how to find or use them (eg proficiency bonus, attack bonus (which isn't an actual term in 5e)).
You also didn't explain how +2 proficiency bonus was gotten to our how that works. This might have helped because the +2 is not correct at all for the level character OP was asking about. You answer also implied to a new eye that it was perhaps static, which is incorrect.
Not defining or explaining the terms makes it more confusing than helpful and this was one of the reasons I downvoted.
Some of it was unnecessary info (if not straight out wrong)
If you have a Feat that provides a bonus (say, the Rogue's "backstab" or whatever they'll calling it now)
There's no such feat in 5e this also displays a distinct lack of expertise. If you don't know "whatever they are calling it these days" perhaps you should leave it out of your answer? Or wait to find the correct name before answering. You may also be confusing the term "feat" with "class feature", two things which are very different and which should not be confused.
Assuming you were actually talking about Sneak Attack, that information does not affect attack rolls at all and was thus completely irrelevant to the question.
if you had some (perhaps clerical?) Feat that gives a bonus when using a bludgeoning weapon
Again, no such feat exists. Not even a clerical class feature actually (though there are a smattering of class features which do something similar, none that I know of do anything with bludgeoning damage).
Displaying wrong and/or incomplete information displays a lack of expertise and thus confidence in your answer and can be a reason to find it less useful (and thus downvote). Especially when you are dealing with new users.
You have to Back it Up
We have an extensive post on what is required for answers as far as evidence goes here. I won't be reiterating what is there (feel free to peruse it at your leisure and ask if there is any specific part of it you find confusing), but I will pull out a couple points relevant to you.
All answers must be backed up. This benefits OP because it shows them that your information is correct and where they can find that information to verify (as well as any additional context and definition those citations might add to your answer). And this benefits you too. If you had backed up your answer and cited things you might have realized that the feats you were talking about don't exist and that your proficiency bonus was wrong for example. It happens to me all the time and luckily most of those errors are filtered out by me consulting the text before posting.
We all make mistakes (and improve our answers to address them)
Every one of us had made mistakes, small or large, in our answers and gotten down voted for it. But votes aren't permanent. Look in your comments for things to improve upon and edit your answer to fix the errors and correct the inclarities. Often, a change sufficient to correct a downvoter's issue will cause them to come back and change their vote or just for more upvotes to come your way.
A good answer
A good answer is one that is clear, factually correct, focused, and well-supported. Answers like that tend to get upvotes, while answers that are unclear, factually incorrect, unfocused, and unsupported tend to get downvotes.