why is it that boots break after three years ?

the boots are bad quality, you wore them too harshly or for too long, your feet got bigger..

Because they're worn out!

Nothing lasts for ever! If you wear them once a year they could last even longer!

Nothing lasts forever

Because you don't wear them enough.
I need new boots every 6 months or so

If you want something to last a long time you have to pay big $. We live in a throw-away society, most things are made of poor quality materials.

to sell new ones

Because you keep stepping on them.

Idk