For a lot of people, this comes down to two issues. First, we've gotten comfortable with brewing and start relaxing on sanitation practices. As we let down our guard, all sorts of microbes can finally sneak their way into our brews and start picking apart our flavor profiles. It is important to always keep religious sanitization practices in mind and get them engrained in your processes.

The second issue revolves around plastic equipment. If you got started with plastic fermenters, after several batches it is time to replace them. They are easy to scratch and with those scratches come homes for microbes. Plastic hoses present a similar problem. These items are relatively cheap in the overall homebrewing picture so spend the money and get new plastic. Or upgrade your bucket to a carboy. As long as you are careful with them (I haven't broken one in 10 years) they will make up your investment quickly. Your bottling bucket can be another source of contamination (in particular the spigot). Take the time to replace these. Your beer will thank you.