Japan still hasn't recovered from the 80s. At some point the economy is going to stop growing. A lot of growth is driven by debt which needs to be repaid. A lot of growth is driven by an increasing population which will eventually plateau, and what's worse you have to support those people (healthcare, education, housing) if you don't want them to cost even more money.
At some point the economy isn't going to just keep growing. I have no idea when that will be, but the market doesn't just go up over time as if it's some law of nature.