Descent isn't the only door
Ancestry is the route most people think to check. It is rarely the only one that applies to them.
Most citizenship-checking starts and ends with one question: "was my grandparent from X?" That is a reasonable place to start - ancestry claims are often the widest-reaching and cheapest to pursue - but treating it as the only question leaves real routes unchecked.
Marriage is the most common alternative. Many countries offer a defined path to citizenship for the spouse of a citizen, usually after a set number of years married and resident, sometimes with a language requirement. It is a slower route than descent where it exists, but it exists far more often than people assume to check for it.
Residence-based naturalization is the broadest route in raw availability: nearly every country will naturalize someone who has lived there long enough, met the residence and language conditions, and passed a character check. It requires time and, usually, having moved already - which makes it the least useful route for someone screening from abroad, but a real one for people who already live somewhere.
Investment and country-specific programs are narrower, but not rare: a number of countries offer defined routes tied to a financial contribution, business activity, or a specific historical or diplomatic relationship. These are worth surfacing precisely because they are not what someone would think to search for on their own.
The point isn’t that ancestry is a lesser route - for people who have it, it usually is the strongest one. The point is that checking only ancestry, when five other route types exist, is how a real option gets missed. A full screening checks every route in the same pass, not the first one that comes to mind.