They then become a piece of history. Statues are a reminder of the past. Whereas nobodys like you and I are simply dust in the wind, forgotten about by all 50 years from now.
Which is why a country and population chooses which statues to construct and which to keep.
The idea that they are sacrosanct forever is nonsense, as you yourself are pointing out there.
People will change their minds, over time, about who should be honoured and who should be memorialized and how and why.
Some will disagree with those.
So, for instance, many cities have decided that honouring people who rebelled against the government in order to preserve slavery shouldn't be honoured.
There are lots of people who disagree. They very much think that the fight to preserve slavery
should be honoured.
But the idea that if the statue goes down the history is erased is silly.
Do you honestly think that if the statue was preserved with something to contextualize it as "this is a lesson we must remember - this man was evil and did bad things we must reject" that the people who objected to the statue coming down would be fine with that?
Of course not.