I disagree with the central point of your post. There are times in history when things DO get worse.
Indeed they do! The whole of history is filled with the rise and fall of empires and civilisations: the Babylonian empire, Ancient Greeks, Roman Empire, the Mayan civilisation and the Aztecs and Incas, Spanish Empire, British Empire.
This cycle of things getting better, and then falling apart, is well established. Rapid expansion; administrative, economic or diminishing resources; internal conflict; loss of social values and cohesion; external pressures; invasion (sometimes); loss of cultural and societal identity.
Spain ruled half the world; look at it now. Britain ruled well over half the world; look at it now (fat, lazy, entitled, unable to fix our roads, even). Ancient Greece outshone the world in science, philosophy, education, mathematics, art, and they invented democracy. Wow! Look at Greece now - effectively a third world country with the good fortune of a beautiful climate and dependent on tourism.
Britain - where I live - is clearly in decline. Why should it be any different from all those historical precedents? In fact, I think the West as a whole will probably decline in the 21st century.
So no, I don't believe each generation thinks the next generation is worse, except in the usual "grumpy old man" way. During the 19th century the wealth of the British population rose precipitously (albeit far less precipitously for the working classes), and there was a great optimism about the future through most of the mid-Victorian era. Science and technology were racing forwards at a rate unheard of, ships, roads, railways..... and money! The future seemed bright. Things began to change in the late Victoria years: economic pressure from Germany and the USA; growing awareness of social injustices; and anxieties around moral decline.
And now, it is very hard to find someone of any age in Britain who is optimistic about the future, especially if they are educated enough to look to Britain's history. And they are right to be pessimistic; there is no chance that Britain can buck the rise-and-fall fate of every civilisation in history.
I think the USA is about a hundred years behind the UK in its cycle, so by the end of this century I suspect it will be facing a downhill future.