Not knowing where you are in Pittsburg, it is hard to explain for your particular location, but here is the general explanation.
Every well has a decline curve that is natural. Think of a balloon starting out really large with a pin prick hole. Over time the pressure and the volume of air in the balloon decrease. The barrels of oil or cubic feet of gas volumes just decrease in a fairly predictable fashion.
The next component is the prices of oil and natural gas. Both were very high last year and especially in 2022 due to the war in Ukraine and recovery from Covid increasing demand. Natural gas prices are very low this year, so if you have a gas well, then that is the majority of your explanation. Declining volumes with declining prices gives lower royalties. The good news is that many experts predict higher natural gas prices next year.
If your dad signed a lease back in the 70’s, then it is likely that it was at a 1/8th (12.5%) royalty or perhaps a 3/16ths (18.75%). Depending upon the wording in the lease, then yes, the lease can hold you for many, many years because it is a valid contract and quite common for the terms that were normal back in the signing day. No sneaking words in, just a valid contract that still holds under the terms no matter who the operator is. We may not like it, but many of us are held by leases like that. Newer leases have more sophisticated terms that can be negotiated.
If it makes you feel any better, I have a well that is about 100 years old and still producing. Over time, we have been quite blessed by it and are grateful for even the low royalties now.
If you want to share the section, township and range and well name, I can show you the decline of your well over time and that will help you visualize it.
You can change the minimum royalty payment with a simple letter. You may have it set at $100. You can get it reset at $25 so you get more frequent checks.