There are a couple of different things going on here.
First, explaining the 76 vs. 19 problem. There are three levels of calculation in Tableau: record-level, aggregate, and table calculation. You've defined the Always on counts as record-level measure, so it returns 19 for each record. There are 4 records for SEC/15-02, so SUM(Always on counts...) = 19+19+19+19 = 76. You could use something like MIN, MAX, AVG, or ATTR as the aggregation to end up with just 19.
Second, blending happens *after* aggregation, not before (like a left-join would). If the blend has both Fiscal Quarter and Primary Architecture as linking dimensions, nothing is returned because there is no "Security" value for Genericarchitecture in the primary data source.
If you turn off Primary Architecture as a linking dimension, then this appears:
The reason why you get a 19 for each is that SUM(Number of Records) from the secondary is performed for each value of Genericarchitecture, since the blend is on only Fquarter.
I'm guessing that maybe the SEC in the primary and Security in the secondary are corresponding values. In that case you could set up a calculated record-level field to use to blend on instead, or you could change the alias for one of them to be the other since Tableau aliases are also evaluated prior to the blend.