I don't think they do this on purpose. They just kind of backed into it - not surprising, since they have no ideology and no ideas of their own, and haven't for a long time. Their voter base is mostly ROC-educated, and brainwashed. To cater to these voters, they've had to "move toward the center", and the center is the ROC worldview. Now some of the younger DPP politicos are ROC-brainwashed themselves. The DPP tried to stop the brainwashing by rewriting textbooks, but this only takes U so far when U don't have a mind of your own.And why even DPP is committed to ROC worldview and Mandarin?
Taking the 400 yrs of Sino-Taiwanese history as a whole, the DPP are just part of a long pattern of half-hearted resistance turning into meaningless compromise and half-hearted struggles to hold onto power, followed by an outside takeover, colonization, more brainwashing, etc. The problem is the "political dependence complex" in the Hoklo psyche. The DPP is just a symptom. Hoklo Yam support for the KMT is just a symptom.
There was a real split up into the 90s. Back then, certain people like newscasters, voice actors and schoolteachers had these stiff, put-on, impeccably rolled, "by-the-book" accents (in Mand) - they sounded like ducks! 95% of "the people" either didn't speak Mand, or spoke blatant "Taiwan Mandarin" or Hakka Mandarin or Southern Mandarin (inc. 閩粵浙 Taros). Granted, there were authentic Northern Chinese too. This changed around the late 90s. The "ducks" and the new adults - 70s babies - moved toward the accent that you hear TW celebrities speaking today, not really rolled, but with zh-/ch-/sh- sounding more like English j, ch, sh in (at least) stressed syllables. The news media is a bit stiffer still, though. Whenever I hear a news media-type talk in real life, I always felt caught off-guard, even in Taipak - and these girls are the kind that never set foot outside Taipak. Kagi and Tailam is just a rumor to them. They spend more time in Paris or Shanghai. The word 天龍 comes to mind.Btw how many people in TW speaking Mandarin "without accent", i.e. like news presenters?
Even today, though, there's still something different about how some young non-Hokkien, non-Canton Taros, esp. in Taipak, speak Mandarin. Kîsi̍t goá púnté mā sī. There's just something in the rhythm, the intonation, the tones, the vowels - rolling isn't required. There's a "Taro sound" which is very hard for Yam women and impossible for Yam men to imitate. Yam girls really like this accent on guys, sometimes subconsciously. Girls with this accent get put on a pedestal - they're classy, they 有氣質.
Another trend started in the 90s - speaking Mandarin (and even Hoklo) with the vowels, consonants and intonation of American English. Next time U see young TWese on TV, notice how some use dark L's like in English. But U won't hear this in a newscast or a telenovela. I call this the Aircraft Carrier accent, b/c like Clinton's aircraft carrier in the Straits in '96, it changed the balance of power and makes it possible for Yams to be powerful and cool w/o imitating Taros.
The thing that really surprises me is how matter-of-fact most Hoklos are about being linguistically inferior. Last yr I had lunch with my ex and her (girl)friend, both Yam Hoklo. The friend was just visiting from mid-island. As soon as we sat down, she commented on how the people in Taipak all had such good accents, so baku. She said, "大概是因為这裡外省人多吧. / I guess it's b/c there's a lot of Taros here." Not a trace of sarcasm or political awareness.
I think Shanghai is the same way. A lot of cities and towns in Taiwan also have bits and pieces of this system. I think something has to be done about it. I think the best solution would be to expand the map. They should take some of the overlapping and redundant 中正 Streets and 民族 Roads south of the old city limits in Pangkiô and Sintiàm, for example, and rename them Cebu Road, Saipan Avenue, Bali Road, Saigon Boulevard, etc. Then go to Lāi'ô· and Lâmkáng and put in an Osaka Rd, a Ryukyu Avenue, even Alaska Street. So on & so forth. Strange, but I think a lot of ROC people would be offended and would try to block this.This morning I saw my mom watching CCTV4. It showed one of its news presenters touring 台北, highlighting that there are 長春路 in its north east part, 杭州路 in its eastern section and so on. She gladly explained that the whole台北 is a miniature of 中國. That must sound ironic to lots of PRCs.