Hi!
I don`t seem to understand this usage of “for”, though I suggest what it might mean. In the given example, the unclear combination of words is underlined:
“He saw where, for want of greater activity in offering goods consigned - quicker communication with shippers and buyers, a better working agreement with surrounding commission men - this house, or, rather, its customers, for it had nothing, endured severe losses.”
for want of suggests through lack of/by reason of it missing/lacking. The word ‘for’ is used here as a preposition and can be used in expressions like: I have failed but it’s not for want of trying. In other words the reason I failed was not because I didn’t try.
For it had nothing the word ‘for’ is used her as a conjunction and has the sense of ‘because’ but is usually used in that meaning in writing rather than in speech.