I agree, our focus should be on the Celestial Kingdom.
Why do the other Kingdoms exist? Because God is in the salvation business, not the condemnation business. He wants to give us the best possible life after the resurrection that we can have. A gift is a gift is a gift. All we choose is how GOOD a gift we are willing to receive. Not everyone is willing to humble themselves. A full third of the hosts of heaven chose NOT to continue on to mortality!! It stands to reason that, due to their influence, many here will not keep their second estate.
The thing I would stress is - WE choose it. WE do, not God!! If we "end-up" in the Terrestrial and Telestial Kingdoms, it will be by a wide margin. We WILL belong in those Kingdoms! Those who suggest that we will be able to progress from Kingdom to Kingdom after we are resurrected do not understand the scriptures. For when we are resurrected, we are resurrected according to the portion of the law we were willing to live here in mortality. Those who obeyed a Celestial Law will be resurrected as inhabitants of THAT Kingdom! Those who obeyed a Terrestial or Telestial law will be resurrected as inhabitants of THOSE Kingdoms! They cannot come up, because they cannot dwell there.
That is what these scriptures mean:
D&C 88: 26, 28-32, 49, 96
26 Wherefore, it shall be sanctified; yea, notwithstanding it shall die, it shall be quickened again, and shall abide the power by which it is quickened, and the righteous shall inherit it.
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28 They who are of a celestial spirit shall receive the same body which was a natural body; even ye shall receive your bodies, and your glory shall be that glory by which your bodies are quickened.
29 Ye who are quickened by a portion of the celestial glory shall then receive of the same, even a fulness.
Which I interpret to mean:
29 Ye who are quickened by a portion of the celestial glory [HERE IN MORTALITY] shall then receive of the same [WHEN YOU ARE RESURRECTED], even a fulness.
30 And they who are quickened by a portion of the terrestrial glory shall then receive of the same, even a fulness.
31 And also
they who are quickened by a portion of the telestial glory shall then receive of the same, even a fulness.
32 And they who remain shall also be quickened; nevertheless, they shall return again to their own place,
to enjoy that which they are willing to receive, because they were not willing to enjoy that which they might have received.
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49 The light shineth in darkness, and the darkness comprehendeth it not; nevertheless, the day shall come when you shall comprehend even God, being quickened in him and by him.
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96 And the saints that are upon the earth, who are alive, shall be quickened and be caught up to meet him.