why the site can't get better data
Do you know about some other source, that would be freely available to use in other tools, such as project-gc.com? If so, please, share the knowledge and I believe we will be very happy to use more accurate elevation data.
The solution of Google Earth is either limited (to 2,500 caches per day) or paid. Refreshing all the caches in database would certainly not fit into the free bucket, but after downloading and caching the data for existing caches, pulling the daily-new ones should be "pretty cheap".
I believe project-gc.com is mainly based on freely available tools and sources unless there is a strict limitation or a other need. I saw some elevation inaccuracies, but nothing significant (though it can be different in other parts of the world).
Using GSAK elevation database could be also an interesting alternative, though it does not speak about the usage policy it can be used for.