People always say the last two halvings caused rallies, but if you look at the timing, it's not true at all. In markets, we don't talk about "catalysts" triggering moves a year later.
In fact, shortly after the 2016 halving, price dropped by 32% over the course of a few weeks!

It would be more accurate to say Bitcoin is simply in a long term uptrend. In fact, since everyone expects upside when the halving occurs, I would expect either downside or sideways. If the crowd is heavily long, price will usually drop. Any successful trader knows the crowd is usually wrong.
I actually thought I was the only one who noticed this. In the previous years that we halved, it was the next year before we even saw a huge bull run at all and like you said, this should not even be considered a catalyst at all when it comes to the movement of the market.
However, I guess for every movement in the market, both uptrend and downtrend; people will always look for one fundamental action to attach to it, even though the market is just moving on its own course based on adoption. I really do not see how halving have been the main cause for market movement and I do not see why people are attaching bullishness to it.