Why would people invest loads of money in BTC after the halving and not before?
People choose to invest in the BTC market post-halving due to a reduction in its supply, which will increase demand, and you know that when supply becomes low and people demand anything high, it increases price pressure.
That is a very common misconception.
First, the supply is not reduced by the halving. Instead, the
increase in supply is reduced. The supply increases with every block until it reaches 21 million.
Second, reducing the supply does not increase the demand, in general. Supply and demand are independent functions.