Because when you vote on any of the platform it impacts your voting power on that platform, plus the other 2 if they are tagged (except steemit...you do not need to use that as a tag). Hits me the hardest on steemit.

When I upvote comments on my steemit posts I try and do it on steemit. I have more control over my voting power. I usually try and use 20%...then on PALNET and NEOXIAN.CITY it will also be a 20% upvote.

When I first started with NEOXIAN.CITY I used a higher percentage to vote. It was then that I realized my steem voting power reduced at a higher rate than I planned.

Hope that helps.