Accuracy of bike rental sample

Not sure if this is the right place to ask. I'm new to ML, and looking at the chart at the bottom of [this page](https://learn.microsoft.com/en-us/dotnet/machine-learning/tutorials/time-series-demand-forecasting), the predicted results look pretty poor to my untrained eye, especially the last few points. Why is this? Would more training values help? I appreciate forecasting is merely that.

Can I also ask, the data in this sample consists of just two columns: "year" and "total rentals". Am I right in saying this algorithm can deal with many columns, and isn't restricted to two?