iNaturalist is a platform for helping to connect people to nature first, and a database second. If iNat caused these people to slow down for a second and pay attention to a non-human organism when they might not have otherwise, then these observations have value. If the observation serves as a reason for helpful, more experienced naturalists to invite the person to take clearer, better-focused pictures in the future, then the observations have value. If receiving that kind of feedback causes the person to look out for the same organism in the future, thereby developing a relationship with a non-human species, then the observation has value.
Do these kinds of positive outcomes happen with every blurry pic of a potted plant? No, but we should always remember that they can. I feel the same frustration with these kinds of contributions, but there’s always more going on than what we can discern from evidence left on the Internet.
And again, the data iNat produces is a byproduct. If it’s messy but people are outside looking at stuff, then the system is fulfilling its purpose. For those of us who care about the utility of the data, we have tools for assessing the data quality of each record, and they handle most situations like the one you describe.