If one day 1 Lisk will be worth like 1 ETH today is it worth giving Lisk for voting? Why is there even a cost for voting?
to avoid spam on the network and support forging delegates by paying a small fee.
All blockchains do this when a transactions are broadcast.
For 10 cent you get thousands of nodes to record 33 of your votes on the blockchain within 10 seconds, and 101 of those get to split that 10 cent.
It's a bargain.

Click, clickety-clik clic....

GO TEAM LISK!