Because this goes back to your understanding of the Holy Trinity. If they're three “co-equal, co-eternal distinct persons", then Jesus is in heaven physically, when he's being with us spiritually that's the Holy Spirit dwelling in us. I simply don't wanna conflate Jesus the Son with the Holy Spirit, because they are two distinct beings. Also, think of the Great Multitude in Rev. 7, that's physically in heaven, isn't it?
They are distinct
persons, but you are making them completely separate beings. And, yes, it very much goes back to the Trinity. Jesus is the Son of God, the Word, the second person of the Trinity in human flesh.
However, it isn't so simple and straight forward, as Jesus's statement that he is in the Father and the Father is in him indicates.
The persons of the Trinity are all the same essence or substance and are can never be separated. It's also why the Holy Spirit is referred to as the Spirit of God, the Spirit of him who raised Jesus from the dead, the Spirit of Christ, the Spirit of his Son, etc., despite remaining distinct from them both. That is, there is such intimacy among the persons, that you cannot have one without having the other two, but they are not all one and the same person.
Joh 10:38 but if I do them, even though you do not believe me, believe the works, that you may know and understand that
the Father is in me and I am in the Father.” (ESV)
Joh 14:10 Do you not believe that
I am in the Father and the Father is in me? The words that I say to you I do not speak on my own authority, but the Father who dwells in me does his works.
Joh 14:11 Believe me that
I am in the Father and the Father is in me, or else believe on account of the works themselves.
...
Joh 14:15 “If you love me,
you will keep my commandments.
Joh 14:16 And I will ask the Father, and he will give you another Helper, to be with you forever,
Joh 14:17 even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him. You know him, for
he dwells with you and will be in you.
Joh 14:18 “I will not leave you as orphans; I will come to you.
Joh 14:19 Yet a little while and the world will see me no more, but you will see me. Because I live, you also will live.
Joh 14:20 In that day you will know that
I am in my Father, and you in me, and I in you.
Joh 14:21
Whoever has my commandments and keeps them, he it is who loves me. And he who loves me will be loved by my Father, and I will love him and
manifest myself to him.”
Joh 14:22 Judas (not Iscariot) said to him, “Lord,
how is it that you will manifest yourself to us, and not to the world?”
Joh 14:23 Jesus answered him, “If anyone loves me, he will keep my word, and my Father will love him, and
we will come to him and make our home with him. (ESV)
Rom 8:9 You, however, are not in the flesh but in the Spirit, if in fact
the Spirit of God dwells in you. Anyone who does not have
the Spirit of Christ does not belong to him.
Rom 8:10 But
if Christ is in you, although the body is dead because of sin, the Spirit is life because of righteousness.
Rom 8:11 If
the Spirit of him who raised Jesus from the dead dwells in you, he who raised Christ Jesus from the dead will also give life to your mortal bodies
through his Spirit who dwells in you. (ESV)
So, we see that Jesus, being physical, says 1) that he is in the Father, 2) that both he and the Father will be in us, and 3) the Holy Spirit will be in us. All three will be in us.
This is just a matter of rhetorics, there're numerous verses that says we're "in Christ", we're member of His church body and Christ himself is the head. The head is not physically "in" the body, but it's always connected with the body and it controls the body, the church body is not decapitated. "We're in Christ" and "Christ in us" both simply indicate that we're in one union with Christ, it feels silly to start a fight over this.
This isn't just a matter of rhetoric. It is important that we try and get things right. It's also important because you claimed someone else was guilty of a false dilemma. But then so are you, as you didn't address the verses they posted, but posted seemingly "opposing" verses. You aren't really addressing anything I've posted either. Instead of taking it all together and making sense of it, you just keep restating your position based on the verses you have given.
There is much more going on spiritually than you seem to want to admit--Jesus is in the Father, the Father is in him, and they make their home within the believer; believers are in Jesus and he in us; the Holy Spirit, also known as the Spirit of Christ and Spirit of God, indwells believers; believers are seated in heaven with Christ; etc.
All that supports the understanding previously given of 2 Cor 13:5:
2Co 13:5 Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?—unless indeed you fail to meet the test! (ESV)
You must make sense both of the clear statements that Jesus lives in us
and that he is physically in heaven. Neither set of passages trumps the other.