Many reasons were suggested: some said that for the One Max to have some of its touted tablet features, it would require the S4 as these features had not yet been developed on the 800; others suggested that HTC simply did not have the capital to purchase or develop the 800 for the One Max and instead resorted back to older S4. Although we may never actually hear the real story regarding this switch, we’re hearing another rumour which says that the switch was necessitated because Qualcomm simply did not want to supply HTC with its current flagship mobile processor. The basis for this rumour is that Qualcomm may not have wanted to risk partnering with HTC as it shows no sign of being able to right the ship yet, thus creating a lot of risk for the processor manufacturer.
Somehow this scenario seems a lot more likely as it seems improbable that HTC would decide to consciously underpower its flagship phablet instead of risking it all on the device that may save them. Then again, this is all just hearsay; what do you think actually happened and if you even believe its true that the HTC One Max is going to ship with the Snapdragon S4 processor.