Some people are rather particular about what’s allowed on their bed, luggage included. Are you one of them?
It’s certainly true that your suitcase has touched all manner of foreign objects on its journeys, but the likelihood of anything actually happening because of it is extremely low. But did you happen to take it into the bathroom with you at the airport? That’s surely a factor. What we’re comfortable with isn’t always entirely rational, and keeping baggage away from where you sleep isn’t too different from removing your shoes once you get home. As ever, it’s probably best to do what puts you at ease as long as it’s within reason.