I think there are a few reasons why this occurs.
1. Different answers for different people
Self-explanatory, we're not the same. Someone who is born with a proclivity for depression is simply not going to think the same way as someone who's generally always happy. There are many very influential nature/nurture differences which lead to different perspectives, needs, values and so on.
2. Different values, interpretations, predictions and so on.
There are many examples to give for each of these things.
Values:
Many topics in philosophy come down to assessing things by assessing the methods and outcomes, to do this, we need to say what is a good method or a good outcome, that is the very simplified version of value. When we talk about these topics where value matters, there are many reasons to value different things. So your answer that something is good and my answer that same thing is bad, we can both be correct according to what we value, correct in valuing that thing by virtue of our sound and valid reasoning and this probably means neither of us has a reason to change our minds.
Interpretation:
We might both agree that society oversexualizes things, we may both agree freedom is good but degrading men and women as sex objects is bad. However, if I think that oversexualising is the byproduct of freedom and don't see it as degrading anyone but you think it is degrading men and women as sex objects, although we value the same things, our interpretations make us disagree on our attitudes towards the oversexualisation that we both agree is taking place. There are many complex reasons that make us think as we do and we may both be right based on our interpretation on what "degrading" means, which neither of us is willing to change our minds on (but with valid and sound reasoning for our positions) and so neither has any reason to change their mind.
Interpretation is a big one really, it's hard to believe you will agree with anyone on anything if you go down the interpretative chain deep enough.
Predictions:
Now here, I think people can be wrong but sometimes it's very hard or impossible to know. Slippery slope arguments are an okay example, if something is not wrong in of itself but I think it will lead to more problems and you think that's a fallacy or that I'm wrong, our conclusions could be very different. Prediction and interpretation are interlinked but predictions deserve their own mention, our reasoning is based on an understanding that isn't necessarily true but it's too complex to know for certain, people have their experiences and biases. This can create premises which lead to disagreements, this is a big one I think, many threads on this forum currently are based on disagreements of what will and will not work as a solution for problems most agree exist and can be fixed.
Well, that's enough for now, there are many reasons. I think that it's important to note that as
@Terrapin Station says, most topics entail a lot of disagreement, I'd say the aforementioned reasons account for a lot of it and can be applied to many different contexts.
It's also important to note that in philosophy, a lot of the fun comes from disagreeing with each other, we like to argue. In business or science, we need to establish very early on what success looks like and try to work through disagreements to get the core results we're looking for. In philosophy, if someone is just agreeing with me, I'll keep extrapolating my position until we find something to argue about and if we ever agree, that's just the end of conversation and I'll move onto a new topic to disagree with people on.