There was not the same level of certainty at the land sale then there is now.
The sale was way before the boom happened, and raised a lot of money to ensure that Splinterlands could survive as a company for much longer.
It also wont destroy SPS, between the Genesis Sports air drop and staked SPS needed to earn SPS rewards around the corner, people will be continuing to accumulate.
RE: SPS Governance Proposal - Begin SPS Reward Payouts for Land Holders