Why does Paul go to such elaborate measures to try and convince the Hutu lieutenant that most of the guests at the Mille Collines Hotel are Europeans?

Because he wanted to protect the Tutsi refugee that he kept in the Hotel. Paul gave refuge to almost 1500 Tutsi people inside Hotel Mille Collines and few Hutus who were not part of the massacre of the Tutsi. During the Rwandan genocides of 1994, the Hutu peasants massacred their Tutsi neighbors leaving more than 800000 men, women and children cut down dead with simple farming tool of the machete. Paul was the manager of the Hotel Mille Collines and he fought desperately to protect his hotel guest including the refugee.

Because his job at the hotel was to keep the guests happy and to ensure safety of those in his care.

Paul was trying to put an end to genocide and to educate people about the Rwandan Genocide and its aftermath. He found a way to save over a thousand people from been murder.

Paul gets his full heart and passion for humanity.

At the end of the crisis, Paul's efforts kept everyone in the Hotel des Milles Collines from being hurt or killed which the result was a huge success.