Why do they try and hide their symptoms of forgetting and losing items and make excuses?

My own (quite extensive) vocabulary is starting to slip. It always seems the nouns that I can’t find, for some reason. I don't try to hide it, I just say ‘bugger, I’ve lost another noun’, but I can’t say that it’s a pleasant new thing!

Fear of loss of control. Fear of being put into a nursing home against their will.

You know when you start talking and then suddenly forget what you were going to say mid sentence? Or when you walk into a room and forget why you went in there. Or you are looking for your keys and they've been in your hand the whole time. Now imagine that happening every day and even worse, and people around you start noticing and bring it up to you. You'd be scared. You'd think "oh my goodness, what's happening to me? I'd better get my act together" and you'd start to try covering it up.

That's why.

Because they’re embarrassed wouldn’t you be?

Because it is embarrassing and you don't want anyone to worry about you.

Because they are no doubt terrified of losing their mind.

Perhaps in the faint hope that whoever is the opposite of "they" will get off "their" back.

Beware victim-blaming. It's never kind or clever.

How would you feel if you realized your grip on reality is slipping, your independence is threatened, and your body and mind are starting to fail you?

That's why.