Motivation I think. He has the type of game where he needs to be highly motivated on the night. Otherwise he's a punchbag.
He's tough but not very polished. I see how he could be outboxed easily if he couldn't get to a guy. And according to the broadcast, it sounded like he had serious management issues early on. Fighting three times in three weeks is ridiculous.
My guess would be he lost due to him giving the earlier rounds away to lead to him falling short when the score goes to the score cards...I admitt that I really never followed Mtagwa's career so its only assumptions on my part but you do raise a very good question.:good
Just not that good. Average skills, average punch. But he has a very good chin and a good aggressive style. Decent fighter to be sure, but a good boxer with some toughness, some stamina and some speed should be able to take a majority of rounds against him. Had Lopez used his jab, moved his head, and not gotten in to stupid exchanges or gotten flustered by the fouls, would have barely dropped 2 rounds, I think. He fought the worst possible way, and nearly paid.