Unfortunately, some apps just require a lot of RAM to run. When you combine the RAM needed to run the basic iPad functions with the RAM needed to run some apps, the iPad1 is just not able to do it, no matter how many times you clear out all running apps or restart/reset the iPad.
Again, in electronics time, the iPad1 is o-l-d. Most developers are developing for the iPads that can handle larger RAM apps. Those that stay with the iPad1 (because it still is a GREAT device) just have to know that some apps just will not run well on it ... or at all.
Marilyn