Yeah, I thought that was weird too. I think that they could have ruled it out if the three pings were done in quick succession. That is, if they pinged her phone three times in a row, maybe it pinged once in one location, once next to that location, and once far away (to where she couldn't have traveled within the amount of time of the pinging). This isn't out of the realm of possibilities. When cell towers get busy, they have been known to kick users to the next available tower. In this case, maybe the nearest tower was far away.
I'm confused about the pings. Some people are talking about pings recorded after she went missing, and they show her as moving. But it also appears there were pings retrieved from her cell provider, recorded when she was out hiking. For example,
"Cell phone pings were recorded near the summit of Vesper Peak, and an eye-witness had lunch with her at the summit around 12pm"
Find Sam Sayers | Resource Center
I'm quite sure LE would have been able to obtain her recent cellphone data as soon as they started looking for her (just to ensure she hadn't returned to her car, for eg).
Pings are more likely to happen when you get to a summit and temporarily connect with a celltower.
The confusion possibly arises out of this quote attributed to Sam's mother:
"A military plane flew over the area during the first two days of the search. Lisa Sayers said they were called in to help locate her daughter’s phone.
“They have the capability to ping a phone that is out of service,” she said. “Because that’s a problem up in mountains. You lose all service. They had two pings that they looked at ... but nothing else has come up."
https://www.huffingtonpost.ca/entry/massive-search-missing-seattle-hiker_us_5b6cbdcde4b0530743c86a33
I can see how it implies the military plane found two pings. I think that would have been very precise info, massively important and reported as such by authorities.
However, it could also be Lisa saying 'The problem with hiking in the mountains is you lose cell service. They (police) obtained her cell data from her provider but they just had two pings (from the day she went missing). They sent a military plane but nothing else has come up.'
I'm not at all sure whether any pings were really recorded after she went missing.