Exactly. No point in extending him if the asking price is 20,000,000. Plus, if that is the actual number that is agent is hearing, why wouldn't he want to hit FA and have a bidding war for his services? This dude has never had a big contract in his career and he is going to turn 31 this year. If San Antonio and Utah both wanted me, I would just let them bid their hearts out and go to the highest bidder. Both teams are great organizations that he is familiar with and both look to contend for titles.
The assumption people are making is that he wants an extension because he said so in the media. A player saying "Nah, I dont want to extend" would be a PR mistake as a fan base would take it as "He doesnt want to be here" and freak out which is basically what happened when D-Will was here.