Taken out of context, there is no difference. "Decreasingly profitable" is an awkward turn of phrase, but it's not ungrammatical.
In an appropriate context -- say, a corporate announcement -- "increasingly less profitable" could be an example if not of actual doublespeak then at least of sugarcoating bad news.
If you say something is decreasingly profitable it's one word with a negative connotation ("decreasingly") against a similar-length word with a positive connotation ("profitable"). "Increasingly less profitable" is two positive words against one small negative word. It sounds more pleasant even though it means exactly the same thing.
Of course no one with half a brain is fooled by this -- but nevertheless this kind of verbiage is ubiquitous.