The absence of an immediate price increase following a Bitcoin halving can be attributed to several factors. While historical data shows that Bitcoin's price often rises after a halving, the timing and magnitude of such increases can vary. Here are some reasons why the price might not have changed significantly one and a half months after a halving:

1. **Market Expectations and Priced In**: The market might have already priced in the halving event well in advance. Traders and investors often anticipate such events and adjust their positions accordingly, leading to price changes before the actual halving occurs.

2. **Market Sentiment and External Factors**: Broader market sentiment, including macroeconomic conditions, regulatory news, and geopolitical events, can significantly impact Bitcoin's price. If these factors are negative, they can overshadow the effects of the halving.

3. **Supply and Demand Dynamics**: While the halving reduces the rate at which new Bitcoin is created, it does not affect the existing supply. If demand does not increase correspondingly, the price may remain stable or even decrease.

4. **Profit-Taking and Market Consolidation**: After a halving, some investors might take profits from any pre-halving price increases, leading to a period of consolidation where the price remains relatively stable before potentially rising again.

5. **Delayed Reaction**: In previous halving events, significant price increases sometimes took several months to materialize. For instance, after the 2016 halving, it took several months before the price saw substantial gains.

6. **Market Maturity**: As the Bitcoin market matures, the reactions to halving events might become less pronounced compared to earlier years. Increased participation from institutional investors and more sophisticated trading strategies can lead to different market dynamics.