Sometimes, as a person grows older and older, their mind begins to break down as senility takes hold of their mind with an increasingly firm grip. In a case like that, it can become easy for them to turn into recluses who hoard things (with animals being a very common thing to be hoarded), and to forsake their own personal hygeine. This personal breakdown is known as Diogenes Syndrome, and it really does not even make all that much sense. It is actually based on an individual who did not practice and sort of hoarding, and who actually might have taken perfectly fine care of his person from a hygeinic perspective. Nonetheless, the name has stuck, for better or worse.
In a person who has Diogenes Syndrome, it is common to collect lots of stuff. This is essentially a person whose mind has latched onto the notion that having a lot of something (really, anything) is a way in which they can stay in this world for just that much longer than if they simply let go of everything and moved on in the “shed the mortal coil” kind of sense. While this is not the kind of thing the real Diogenes would have done, since he was a transient guy who lived in a wine barrel, it does speak of a lot of homeless people in the modern age.
Another common trait that characterizes the Diogenes inspired person is an unfortunate tendency to no longer take care of themselves. In many cases, this leads to teeth which are in terrible condition, to not bathing very often (or at all), and even to no longer tending to their hindquarters when they have used the restroom. Again, the real Diogenes was most likely not a nasty individual. But for however he actually was, it is possible that someone really did not like him- because in this day and age, he is remembered in this particular way.