Such 'up' phrasal verbs as wake up, write up, end up and so on date back to at least the 1100s in English, with 'give up', meaning 'surrender' being the oldest recorded. There are many of them that appear to have no rhyme or reason behind them, since they appear to have no 'directional' quality to them whatever. And there is further confusion in that, in several cases, the 'up' can be replaced by 'down'. "It's up to you" means pretty-well exactly the same as "It's down to you" in certain situations in modern British usage, for example.
Here's a nice quote that sums up - geddit?! - the situation...
"If you're up to it, you might try building up a list of the many ways in which 'up' is used. It may take up a lot of your time but if you don't give up, you may wind up with a thousand."
The simple answer, therefore, is that there is no real relevance other than the great god 'usage'. It's here to stay!