I disagree with you that bitcoin price is easy to predict in the long run because nobody knows what Thebes future has fod bitcoin which is the main reason why you are advised to invest with the amount of money that you can afford to lose. Just the way that the price is unpredictable due to Thebes volatile nature of bitcoin is the same in both short term and long-term, if not those early bitcoin hodlers who sold too early when bitcoin price increased to $10k wouldn't sell but should know that bitcoin price will hit $120k in future.

Bitcoin is price increases based on increase in adoption and the halving event but that doesn't mean that you can actually know the exact price that bitcoin will reach in the year 2029. You are advised to invest in the long-term because that's the only way to limit the risk in bitcoin investment because the price increases overtime based on history data since bitcoin is still in her early stage.