Why do floating-point numbers even exist

http://ta.twi.tudelft.nl/nw/users/vuik/wi211/disasters.html
Why is it so hard for CPU-making Jews to implement fast arbitrary-precision arithmetic or at least fixed-point numbers?

It's interesting to think about some of the problems that proper arbitrary precision could solve ... encoding unicode codepoints, coping with larger file sizes, etc. I'm more interested in its uses for representing integers than rational numbers.

I guess UTF-8 could be used to represent arbitrary precision values?