It was accepted by a mainstream audience.

It got to No 2 in the British charts & No 11 in the American charts.

So did a couple Metallica albums.

So?

Why shouldn't pop music be sophisticated or experimental?

The fact is it sold well and it influenced the shape of pop in the coming years. So why isn't it a pop album?

Because there have to be lines when it comes to classifying music as a certain genre. That album just about crosses it so I don't consider it a pop album.

It's not like that sort of music was totally alien to a mainstream audience at the time.
Kraftwerk & Brian Eno were hugely successful by then, even Can were getting into the charts.
Bowie used that and made it even more accessible by incorporating that into his sound. I don't think it was any different to him using jazz on Aladdin Sane or soul on Young Americans.

Ok, fair enough. I was thinking more along the lines of Bowie's other work, and he has definitely made albums far more pop oriented than Low (to say the least). Let's Dance comes to mind.

1 - Depeche Mode - Violator
2 - Tangerine Dream - Optical Race
3 - Recoil - Selected
4 - Terranova - Digital Tenderness
5 - Dataraper - Naught man's land

I like pop song in following

1) Break your heart

2) Nothing on you

3) Hey soul sister

4) In my head

5) Rude boy

Top 5 pop Albums:
1. IN-A-GADDA-DA-VIDA Iron Butterfly Atco
2. HAIR Original Cast RCA
3. BLOOD, SWEAT & TEARS Blood, Sweat & Tears Columbia
4. BAYOU COUNTRY Creedence Clearwater Revival Fantasy
5. LED ZEPPELIN Led Zeppelin Atlantic

5. The Seeds of Love-Tears for Fears
4. The Wind In The Wires-Patrick Wolf
3. Hunky Dory-David Bowie
2. Viva Hate-Morrissey
1. Sgt. Peppers Lonely Hearts Club Band-The Beatles