What is the most likely reason that Phileas Fogg spent so much time alone?

Fogg preferred his own company to that of others..... in my opinion, he enjoyed being an enigma.

Phileas Fogg was not known to have either wife or children, which may happen to the most honest people; either relatives or near friends, which is certainly more unusual. He lived alone in his house in Saville Row, whither none penetrated. A single domestic sufficed to serve him. He breakfasted and dined at the club, at hours mathematically fixed, in the same room, at the same table, never taking his meals with other members, much less bringing a guest with him; and went home at exactly midnight, only to retire at once to bed. He never used the cosy chambers which the Reform provides for its favoured members. He passed ten hours out of the twenty-four in Saville Row, either in sleeping or making his toilet. When he chose to take a walk it was with a regular step in the entrance hall with its mosaic flooring, or in the circular gallery with its dome supported by twenty red porphyry Ionic columns, and illumined by blue painted windows. When he breakfasted or dined all the resources of the club—its kitchens and pantries, its buttery and dairy—aided to crowd his table with their most succulent stores; he was served by the gravest waiters, in dress coats, and shoes with swan-skin soles, who proffered the viands in special porcelain, and on the finest linen; club decanters, of a lost mould, contained his sherry, his port, and his cinnamon-spiced claret; while his beverages were refreshingly cooled with ice, brought at great cost from the American lakes.

If to live in this style is to be eccentric, it must be confessed that there is something good in eccentricity.