Why did this bread not expand properly?
Most of the expansion did occur at your score, and you got a good rise, so I think you should not be too disheartened! It looks like you cut diagonally rather than downwards: this works well for rolls and smaller loaves, but I'd suggest the simpler cut for a full pan loaf. Scoring techniques are discussed here: https://food52.com/blog/13136-how-to-make-pretty-bread-like-a-pro.
For loafs baked in pans, I suggest making multiple diagonal scores across the top. I find this more attractive than a longitudinal scoring, and it also gives more places for the dough to expand.
Generally it is important to knead (or stretch and fold) the dough quite thoroughly before it proofs. This removes any large air pockets and ensures the remaining air is evenly distributed through the loaf. If you underproof the loaf then it may expand in unexpected ways in the oven, breaking through the skin. I recommend the 'poke' test.
Finally, you might try turning down the temperature slightly in the first 20 minutes: if the oven is too hot then the outside of the dough sets before the inside has finished expanding, causing unpredictable ruptures.