Key:
It's in the vowels
Explanation:
Samsara words contain multiple sets of identical vowels which are repeated with the same spacing: pIpElInE (IE-IE), AvErAgE (AE-AE), spOkEswOmEn (OE-OE), AntEjUrAmEntUm (AEU-AEU), etc.
Note:
As @el-guest pointed out, some of the non-samsaran words also fit this pattern (adequate, dilapidated), but they contain other vowels that are not repeated. Samsaran words contain exclusively repeated vowels.
Title:
Perhaps they are called Samsara words because Samsara is a repeated cycle of birth and death