Why is bitcoin written in C++? What made the core developers choose C++ as the main programming language for implementing bitcoin? Was this because of their personal preference? Or another reason?
The most important reason is that the original Satoshi codebase was written in C++. A system like Bitcoin has extremely strong requirements about consistency in behaviour: all nodes on the network must accept and reject the exact same blocks, or we risk a fork. The first choice to avoid bugs that risk introducing inconsistency is to not rewrite the code from scratch.

Although all programming languages have flaws, and C++ is no exception, there are various reasons that make it an appropriate choice. An easily-overlooked one is that it provides very tight control over memory usage. Many modern languages (especially those that rely on garbage collection) make it hard if not impossible to reason about tight bounds of memory usage. Since Bitcoin Core is a security-critical application that is directly exposed to the Internet, it is nontrivial to guarantee that there is no way to trigger it to allocate large amounts of memory, thrashing the machine's swap space, or worse, killing the process.

This is in addition to a good balance between high-level where desired but also many avenues for performance optimization. Performance may be more important than is immediately obvious, as the convergence of the network relies on quick validation and propagation of blocks. If blocks take too long to validate compared to their creation frequency, economic factors start to unfairly advantage larger/faster miners (see the Selfish Mining attack, for example). Under extreme conditions, if blocks would take ~minutes to validate, the network may fail to converge at all, as nodes simply don't hear about blocks in time anymore.