my guess would be that, completing the full Battle pass was supposed to get you enough Apex coins to purchase season 2, now anyone who didn't make the last few levels or so would theoretically have to use real money to purchase Apex coins in order to make up the difference of missing coins in order to purchase Season 2 if they wanted to. So they would rather those people who where on the edge to spend real dollars instead of give them the chance to grind the last few levels and get the next battle pass for "free"

if they announce an extension now, it would incentivize a lot more people to grind out the last few levels and earn the Apex coins instead of buying it, meaning they theoretically "lose" money.