If you're in the majority, you have the votes to be able to accomplish something with reform. It's not like we live in a monarchy, reform is possible under our system.
If reform isn't working to bring about your goals, either your goals aren't popular enough, or they are popular but the people lack the will and organization to vote for them.
If the people lack the will and organization to vote effectively, they certainly lack the will and organization to topple the government.
My area of expertise is managing complex systems and change implementation. I sincerely don't understand how revolution is supposed to work where reform doesn't. No one has been able to give me an answer that doesn't bill down to idealistic hope. How is this revolution supposed to be implemented, and why can't we build the foundation for revolution while simultaneously using the tools we have for reform? Wouldn't widespread support for reform be the best possible proof of consensus?
Other comrades already gave pretty good answers, but I want to say that you're not taking propaganda into account.
From the day we are born to the day we die, we are bombarded with capitalistic propaganda about how it is the only viable system, how you can "win" too and how "awful and evil" communism and communist leaders are/were. We can't expect the general population to want anything other than reform when that is what is taught all the time as the only solution, and yet despite that, we only see things getting worse and worse.
Reform is not the solution because the whole system is made for the bourgeoisie. Reform is like trying to use a band-aid on an open wound, when in reality it needs proper treatment. If reform was capable of achieving socialism/communism, we wouldn't constantly see the erosion of rights and social nets everywhere. You can fight for a right for decades all to have it taken away the moment someone else comes to power. Not only that, but you also have the issue of lobbying. And like other comrades already mentioned, this is even worse in the global south, as every time a proper reformist or even socialist leader is elected, they get assassinated and/or the nation gets coup'd.
The unfortunate reality of the situation is that, even in the global north, the moment the people vote for anyone that threatens capital, the ruling class will not sit idly and hand over the keys to the working class, they will fight to keep their gripe. The only way they will give concessions willingly is when you have the threat of revolution at the horizon, and they only do that to appease the masses in an effort to destroy the possibility of the revolution happening. They give up their rings not to lose their fingers.