There is the small matter that both Plato and Aristotle left behind a substantially well-documented record of their existence, not to mention things (at least ostensibly) authored by them.
Jesus's life, although enthusiastically chronicled in the Bible, does not have the advantage of retaining anything authored by the man himself, although there is a record of what he said or did at various times and places.
There's also the fact that neither Plato nor Aristotle, nor any of their followers made any kind of claims as to their divinity, any miracles that they performed, or ressurrection from the grave after three days, etc. Nobody celebrates any religious holidays based on either of them, or has spilled blood or persecuted anyone over their philosophical conjectures.
Whether you are a believer, person of faith, etc. or not, it's hard not to notice that the historical accounts of Jesus and his life serve not just as historical "fact" or "evidence", but that they also promote a very distinct agenda, particularly the farther back in history one looks. It's nautral for there to be a greater level of skepticism and doubt about Jesus' life mostly because the stakes are a helluva lot higher than they are in disputing Mssrs. Plato and Aristotle.
Sure, you can raise reasonable doubts about the existence of any historical figure, especially in the BC era. But let's not for a minute suppose that we can compare Jesus to Plato and Aristotle in terms of the significance of the issue, or in terms of reasonable doubts based on the record.