I cannot answer particularly for Glasscock, but the general answer is location, location, location and economics. The operators will drill where they are pretty certain that they will make a profit. Depends upon rigs availability, crews availability, reservoir quality compared to their total portfolio, price of oil and gas, takeaway capacity, availability of supplies such as pipe and chemicals, etc. The operators go where the money will be.
Your original lease wording determines the terms for how long a lease is in effect. Yes, depending upon the wording, a lease can hold your minerals for decades by being in production. I have one that is a hundred years old. Many of us later generations are held by those old leases. They are a solid legal document. They can drill more wells, but they do not have to unless you have a “continuous drilling” clause.