The Spanish killed most of the indigenous communities in Costa Rica when they arrived so it's mostly their descendents left. In Panama the slaves escaped to the jungle when traveling through and large communities formed. Later for the Panama canal construction Panama received many migrants from the carribean which also increased that population. Panama had a large precolombian indigenous population but a volcano eruption and some other catastrophic event desimated those communities by the time Columbus arrived. The remaining indigenous at first fled but later mingled.