1. old age/Father Time - inevitable, every athlete needs to retire
2. ring rust - out for two years
3. not enough time to prepare for a replacement fighter - no game plan for Ugas, just go there and do your best
4. overtrain - he took extra rounds because he is anticipating a fight with Spence
5. Ugas at the prime of his career
This is not an excuse. Just finding out the possible reason.
I will grade your observation as all of the above, number 3 is the main reason remember Manny's first fight in Vegas back in 2001 he was also a replacement took 7 days notice and his opponent does not know what to expect from him in the ring and he is fighting a very classy fighter in Ledwaba, this is also what happens to Manny he prepared for Spence and he cannot adjust to Ugas fighting style because of lack of time.