A blockage in the plumbing is to blame for a sink that takes forever to empty. Regardless of how big or small the obstruction is, it must be fixed immediately. You may have a major clog that will lead to pipe failure and flooding.
Overuse of drain cleaning chemicals can damage plumbing. They might speed up the pipes' degeneration.
Repiping your home is an option if you constantly fix the plumbing. It's more cost-effective in the long term than constant maintenance. If you want to know if your home needs new pipes, you should consult a professional plumber.