Welcome to the site !!
It could be a couple of things ....... Did you try the enriching knob ?? (the idle knob , you pull it for cold weather starts) , this might tell you if it is a fuel issue or a ignition issue ....... As far as the kill switch , it still could have had moisture in it , and from sitting it has now corroded and that is hampering the starting because of the weak spark .... I would think after sitting for a couple weeks that any moisture that was in a plug in connection would have dried , but that does not mean that the moisture that was in there did not cause damage , if that were the case , then all those that have gotten water in the kill switches could simply have cleaned them and been running again , but ultimately , they have almost all had to replace the switch
A 1 gallon ziploc bag with a trash bag tie will prevent this from being a issue , and is what I do when I wash my 20 450R , i tried wrapping cling wrap and it still allows moisture to get thru , the ziploc bag is heavy enough to keep the moisture out even with a pressure washer spray applied directly to it but I would also use the tie wrap tightly at the opening to completely eliminate any moisture or steam from entering ..... I would still lean towards the kill switch as the issue , simply because it was running fine (as per your explanation) prior to the washing , though it is possible the ECM or Stator has gone bad , I would focus on the cheaper possible "fixes" first , cheapest being replacing the kill switch ( they are not cheap , but far less expensive than a ECU or Stator *about $80.00*) , since you said it ran after the cleaning , I would think that the spark plug is still good , but the weak spark is the main concern and most likely caused from within the switch .....
But that is where I would start , it is a common issue with the new gen bikes .... why a dirtbike can't get wet is beyond me , but I guess that is how they sell parts ...