Not a specific comment on the Mikes Bikes / Specialized contract, but it is very common in contracts to have change of control provisions that allow both parties to terminate the agreement upon change of control for the other party. This is so that if your competitor purchases a company you are doing business with, you don’t have to continue to do business with your competitor and thereby provide them what could be proprietary information.
On the other hand, if you are smart, you write provisions so that key suppliers cannot terminate in case of change of control of your business, for exactly the reason in this case. That is, if a significant value of your business is dependent upon company Q, then you wouldn’t want a clause in your agreement with Company Q that allows them to terminate your agreement if you are acquired, or the value of your business would be significantly impaired - effectively you would have to run any possible change of control by company Q to make sure they wouldn’t terminate your agreement.
But my guess in this case is that PONS knew this was going to happen, and factored it into the price they paid to acquire Mikes Bikes. They might have even been counting (this is rank speculation) on Specialized to terminate the agreement in just a manner like this, so that Specialized would get bad publicity. And when Specialized bikes were replaced in Mikes Bikes by PONS brands, consumers would blame Specialized.