What classical computers lack in quantum-ness, programmers can make up for with cleverness. With mathematical techniques, some problems that look rooted in quantum processes could be “de-quantized” and simulated efficiently with classical computers. It’s not really clear why some algorithms are easy to rearrange and simulate classically while others aren’t, though it appears that the less entanglement is part of the problem, the more likely it is that computer scientists can manipulate it and run it efficiently on a classical computer. Sometimes though research into quantum computing can lead to breakthroughs for their classical counterparts. In fact one problem that was thought uniquely suited to quantum computers was recently shown to be solvable with classical computers as well.
Quantum computers still have a long way to go before they can claim quantum supremacy. Unless we develop room temperature superconductors, quantum computers are going to have to be kept in ultra cold environments to function. That means that classical computers aren’t going anywhere anytime soon, but they may get better thanks to competition from their quantum rivals.