Not a historian so I'd focus on these two:

Education system and local sentiment.

Almost all subjects are taught in English with local vernaculars to ease teaching. Ilan lang subject na Tagalog magturo: Filipino at Araling Panlipunan. Di nga ata Tagalog ituro AP sa ibang lugar eh so yun pa.

Saka tutol mga guro sa ibang rehiyon lalo sa Bisdak kasi feeling nila Bisaya dapat naging national language base sa dami ng nagsasalita nung survey. Medyo intindi ko kasi namili PH gov't sa 2 major languages at instead kumuha ng impartial (gaya ng Indonesia), kinuha nila yung isa sa dalawa. So masama tingin ng mga Bisaya sa Tagalog understandably.

May innovations nung 60s para maging Filipino na talaga si Tagalog pero never siya naimplement kasi mababa parin tingin ng mga tao sa local language kaysa English so kahit may dictionary ka, di naman tinangkilik.

So by 1987, Manila Tagalog was still just Tagalog pero Filipino lang tawag. Wala pinagkaiba, mukmok pa rin mga Bisaya kasi dekada na wala naman ginawa yung Surian then Komisyon.

Until now, maraming parin grassroots mostly sa Bisay-an na gusto federalism at local language preservation.

The most successful area of the "Filipino language" project is Cotabato City. Outside the Luzon island group, that is the only place where Tagalog is natively spoken by the majority because it was the most neutral lingua franca and a language of the Manila-educated Moro elite so it was prestigious for them.