The thought that someone has to worship "as their ancestors did" always surprised me. If people can change, and social structures can change, why not gods and rituals?One of the main points to reconstructionist pagan religion is worshipping within the cultural matrix that the gods were being addressed in when their traditions flourished the first time. Mapping the rituals directly to how it was done in the past is occasionally awkward for the well-documented traditions and impossible for others. But there are good reasons to do it to the best of our ability for those of us who feel the need to do so. And as the gods have had some hand in the situation, guessing at their motives isn't too far out of line.
Starting from the presumption that gods change because people change, it would easily follow that gods, like people, are creatures of habit. One doesn't exist without the other. They get used to certain things being done in certain ways. Some are more prone to accept innovation than others. Attempting some degree of continuity to the older approaches gives the god something familiar to work with and grants the practitioner a certain degree of contact with tradition. When dealing with a cultural matrix other than the one someone was raised in, the contact helps deepen their understanding of that culture. This is not a reason to remain hidebound, but it is a reason to base their innovations on their best understanding of the root culture.
Putting it another way, while the gods may be fine with the new and different, they may also get nostalgic for the older ways. People have nostalgia fits all the time. It would then follow that some people would be led to follow the gods in a way that at least somewhat approximates the original forms of worship. Plenty of people will invoke gods into rituals that have little or nothing in common with the ways those gods were first dealt with. If nobody tried for the older ways, the new ones would be all the gods ever received. It might be fine for some, but I highly doubt all of them are that flexible. Most humans aren't, especially if they didn't choose their displacement. From where I sit, gods are closer to forcibly emigrated people than voluntary ex-patriates as a rule if their pagan roots have been stepped away from by any form of coercion. If you're away from home because of reasons outside your control and the new system has little room for you, reminders of what you used to take comfort in will matter.
This is why I think the gods respond both to the new and the attempts at the old. The innovators who approach the gods from outside their original culture at least call their names and pay attention to them regardless of the familiarity of the framework. Those who strive toward the older ways carry some version of the gods' old reality they can recognize. In tandem, the gods get a fair amount of attention they'd lack otherwise.
The above is no excuse to claim a new ritual is ancient. But it is part of why people strive for it. The reasons people are willing to lie about their rituals and others are willing to believe them is a topic for another post.