Sprint is sitting out the incentive auction because 600 MHz airwaves are “spectrum of the past,” CFO Tarek Robbiati said this morning.

The nation’s fourth-largest operator is the only major carrier not participating in the incentive auction, which will move to a third round of bidding from wireless companies next week. While 600 MHz has been described as “beachfront spectrum” for its propagation characteristics, Robbiati said it isn’t ideal for delivering increased capacity as wireless data consumption continues to soar.

That—and not a lack of cash—is why Sprint opted not to participate, Robbiati said during an investors conference.

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“We did not participate in the 600 MHz (auction) not because we didn’t have money at the time, or we were under-resourced for it,” he said. “It is simply spectrum that is spectrum of the past. The world is moving toward high-capacity wireless data networks, and in that world the best and most efficient spectrum that is needed for that… is mid-band spectrum, the spectrum that we have, the 2.5 GHz spectrum.”

Robbiati also noted that the TV broadcasters’ airwaves currently up for grabs may not be available for several years. The FCC has issued a 39-month repacking plan for that spectrum, enabling the broadcasters to move to other airwaves while their former spectrum is reshuffled for wireless use.

“Why invest in 600 MHz spectrum if that spectrum doesn’t really cater for the future, and also it’s spectrum you cannot deploy for four years?” Robbiati asked rhetorically. “And it doesn’t have an ecosystem in support as widespread as 2.5 spectrum, which is the largest ecosystem in the world.”

While some may view Robbiati’s comments as sour grapes, the value of mid-band spectrum appears to have risen recently because of its ability to provide increased capacity. And the value of 600 MHz airwaves has increasingly been questioned as the FCC’s auction has yet to produce the sky-high bidding some had hoped for.

Stage 2 of the auction ended after a single round of bidding generated only $21.5 billion for the spectrum, far short of the $54.6 billion that was necessary to end the event. Some onlookers had predicted that proceeds from the event would surpass the record $44.9 billion generated by the auction of AWS-3 spectrum that ended in January 2015, and FCC Chairman Tom Wheeler said earlier this year he expected to see a “spectrum extravaganza” as companies vied for airwaves to meet ever-increasing demand for mobile data.

“The bid-ask between what the broadcasters want and what the operators are willing to pay continues to be quite wide,” Barclays analysts wrote last month in a research note. Whether that gap will close significantly during the third stage is anybody’s guess.