Fatty liquid vs non fatty liquid in dough
The reason that your enriched bread handled completely different than your initial bread is because eggs, sugar, and oil all inhibit the formation of gluten. Sugar attracts water, so it competes with the proteins gliadin and glutenin in flour for binding to water (glutenin+water+gliadin= gluten) added to the mixture. 

Egg Yolks contain a high percentage of fat and liquid oil by definition is 100% fat. Fat uses a different mechanism than sugar to inhibit gluten formation. Fats coat the individual gliadin and glutenin proteins. Because fats are hydrophobic (not attracted to water) they effectively shield the gliadin and glutenin from water, which inhibits gluten formation.

With this collective reduction in gluten, the bread becomes much denser because the carbon dioxide produced by the yeast doesn't have enough gluten to use for expansion of the bread. If all other ingredients and factors were the same between your initial and enriched bread recipes, but you increased the amounts of sugar and fat the result is a denser bread.