I guess it falls in the free speech category. I don't like what you say but I support your right to do it.
HOA residents also have the right to make binging agreements, for better or worse.
To the extent I care, it is a mater of aesthetics. I enjoy seeing a less cluttered and more maintained environment. Because they are my neighbor, I see their front yard frequently, as do my visitors.
This is basically the same reason that I don't like it when people litter and leave their garbage in the street, or I don't leave dirty dishes around my house.