Is there a good reason that you cannot extend a future arb eligible player during the previous year?

You can extend free agents, but not arb eligible players.  It doesn't seem to make sense unless I am missing something.  I have a guy who has had 1 arb year that I would like to sign to a 2-3 year deal, but it will not let you negotiate with those players.

Seems if you can negotiate extensions with Free Agents, you should be able to with Arb eligibles. 

My 2 cents. I know you can sign them long term the day before the arbitration day, but still I'd like the option to do this the year before so I can lock up the guys in advance. 

Because people would arb them three times and then try to sign extensions.   Maybe they could program it so that you can't do it after the third arb but it seems like a clusterF waiting to happen with the players who weren't arb-el until after 4 pro seasons. Or the ones who go to arb the first time and ask for 378k.

They already have it programmed so guys who go to arb 3x will not sign free agent contracts. So this is a non-factor, would only be an issue at second Arb. 

You're negotiating an extension.  So it's still a factor as you can't do that with 1st/2nd/3rd year arbs now. 

Thats what I am arguing they change. They allow it for 1st and 2nd arbs.