Why are there so any apps on an iPad or smart phone that you might not ever use?

I suppose many do use them. And possibly they get paid to develop new phones etc. by the companies of those apps?
Worst are the ones you cannot delete like for instance Xiaomi's own apps.
Now I don't mind too much, I don't use Apps anyways, do everything on PC. I do need WhatsApp installed on my phone so I can use it on the PC.
And I installed VLC app myself to play music as the one on the phone was by Xiaomi and it suxed.

So they can spy on you

The same reason Microsoft Edge keeps opening on my computer when I don't want it to.

Spying on me would be in vain since I don’t do or say much.

I think you can disable unwanted default apps which may not be uninstalled, and turn off unnecessary access permissions of the others.

I don’t touch the ones I don’t use and really see no sense in disabling them since it’s my iPad and the only one who uses it.

Apps take up memory space, the more you add the less space you have available for other things, so don't add any extra ones you don't need in my opinion.

When you have a friend over,
Put your tablet/ipad/phone in the same room but don't use it...

Then say something specific, out loud to your friend...

Like...
I'm thinking of buying a new car
I'm thinking of buying a diamond ring
I'm thinking of booking a holiday

And note how you start seeing adverts for the very things you mentioned...

I rarely have friends over that stay for certain amount of time and so saying those 3 lines would be in vain since none of them I would discuss. Yes I only add on apps that I would use.

That might be the case if one grants the app, which is displaying the ads, permission to access the microphone.

Where’s the microphone located on my iPad?

This page shows where the mic is.

https://www.lifewire.com/does-ipad-have-microphone-5218260

Even if you don't have friends over, just say something out loud in the same room as your ipad/device...

Like...
Gosh I need to buy a new car

And watch how you start receiving adverts for cars...

Let’s see I only have an ID card and not a drivers license so buying a car would do me no good. I live with my parents so mom is my ride.

and no matter how hard you try you can't get rid of it