I see a lot of people here either ignore or fundamentally misunderstand the facts.
The owners are quite content to do long-term contracts, as long as they're undervalued and retain team control with no opt-out. That is what has been on the table. Harper and Machado have never had a negotiation as MLB players and are looking to use their leverage during one of two (at most) times they will be able to use it. 10/300 is laughable for Harper without an opt-out clause--he is worth more during the front half of the contract, and with the revenue trends, possibly even on the back half even with age regression. We are in an era where because of the current CBA, there are players under team control for over 14 years.
The idea that agents make more by convincing them to hold out is also laughable. Harper signing for, say, 4/140 is going to offer more opportunity for more money over the next ten seasons than the current offer. An opt-out on 10/300 has the same safety valve.