Kind sad sad how we have the tendency to equal success with wealth. There are way more ways to be successful than money, or fame (and hey Shackleton is one of the big four arctic / antarctic explorers, so fame-wise he did good).
I would agree with you today but at that time his wife and family would have been reliant on his income in a way that isn't true now. If you consider her and his responsibility to her then this attitude becomes quite selfish. Keep in mind he accepted this responsibility when taking on the marriage.
I wouldn't outright call him a failure, no, and I wasn't doing that. But I do believe it's healthy for us today to examine ways that women were disadvantaged in the past if we want to fight against such things in the future.
If his wife was dismayed by his unwillingness to fulfil his promises then we could in fact say he was a failure in that way. Whether you choose to look at it that way or not is of course up to you. At the end of the day he took on the responsibility of supporting other people in a material sense and then chose to prioritise his own good feelings over that support. The issue is of course systemic at the core, in that she was limited in her choices, but he understood this when agreeing to marry.
I agree with you that things in the US are not as good today as they could be in ensuring that people can live independently, but the freedom of women to support themselves is certainly much improved in the last 100 years. I also have to say that the US is not the whole world and Shakleton and his family were in fact normally based in British territories where the modern welfare system is significantly more developed.
Much to his wife's dismay.