It's not very fair to say "I'll only believe that an esoteric motivation exists if the party motivated by it explicitly states that publicly."
(By esoteric motivation, I mean either an "underlying" motivation or an "epiphenomenon" that feeds back onto itself.)
It is not necessary to acknowledge or even to know that you are behaving as part of some esoteric motivation, for it to be either a true or at least useful model. For example, think of "selfish gene" type explanation of reproductive / behavioral biology. That is a useful model for thinking about behavior even if the parties themselves talk about courtly love, religious morality, etc.
Particularly in the case of a highly developed financial economy, there are lots of decisions that have effects, which effects tend to reinforce making those decisions, without anyone explicitly talking about those effects.
For example, the political decision to create and maintain the tax-deferral advantages of e.g. 401k accounts, is bipartisan and widely touted as helping to advance the cause of retirement security and broad prosperity. However, in a very real way, it's also about shunting vast quantities of "dumb money" into a relatively high-fee intermediary industry of 401k administration, mutual fund management, and etc. In turn, those intermediaries employ vast numbers of well paid personnel, as well as enjoy concentrated financial returns to their ownership -- and the owners and workers of the intermediaries lend massive poltiical support to perpetuating and extending those types of program (see e.g. the successive creation of more and more favored account types: Roth IRAs, 529s, Coverdell ESAs,
HSAs, FSAs, etc. etc.). This means that Congress is compelling the nation at large to turn over a higher % of GDP to financial intermediaries.
It would be disingenuous to claim to disbelieve this unless a Senator stood up and said his goal is to "turn over a higher % of GDP to financial intermediaries." That is certainly not his exoteric goal and probably not even something that he thinks about. But it is a very real consequence, and the feedback loop from the beneficiaries (lobbying, jobs, contributions) most certainly influences him and makes it "about" that.