The main purpose for NANO to compete with blockchain in term of feeless payment system compared with the blockchain. DAG being created caused by the creator of DAG was feeling blockchain is not the best to handle massive transaction due to the high fees. that's why there was a system called DAG that used server as a validator but this is totally centralized.
NANO will never become a store of value like bitcoin. Both were different.
NANO is only to be used for the micropayment system only