Suppress your fandom of Brasil '66 for a moment and try to look at this as someone in their late teens or early 20s […]:
That's death, right there. I personally love Andy Williams and Sergio (and I had a massive crush on Lani)---but even if the group could have somehow made themselves as 1970-hip-now as the "Stillness" album cover suggested, nobody was gonna buy it coming from them.
I wonder if Michael's perspective and insights on this matter would have only been possible after-the-fact (with the benefit of hind-sight / in-retrospect).
I suppose Sergio, or his manager, or A&M marketing (or whoever it was who made these decisions for how to promote the band and its music) were trying (I assume that their strategy was) to appeal to a broad array of demographics. The TV appearances seem to reflect such an approach.
For one thing, Sergio had a connection with Andy Williams (That's where he got Janis Hansen from) (correct?).
The Music Scene show on ABC had a lot of the younger, hipper Soul and Rock acts -- and the footage that I see seems to be mostly live -- whereas, B'66's appearance was largely mimed (albeit with live acoustic piano on "Lineman").
I suppose B'66 looked out-of-place in that context (by 1969).
But, there is footage on INA (French) TV that is live doing a fast-tempo rendition of Edu Lobo's "Upa Neguino" -- no orchestration. To my ears (in the 21st century) it seems like hip, cutting-edge Brasilian M.P.B. and not any old lounge Jazz Bossa Nova (the way the American mainstream maybe have perceived that).