OT: Options

I just noticed something about SPX options versus SPY options that at first surprised me, although then I rationalized it.
Maybe an expert could offer their opinion, in case I'm totally off-base?

The thing that suprised me is that for SPY options the ask is always greater than IV (intrinsic value), and understandably so because otherwise there'd be an arbitrage opportunity (see below).

But for SPX options, ask is not always greater than IV (it can be, but doesn't have to be).
I *think* the point is that you can't hold, i.e. buy or sell SPX 'shares', whereas you can hold SPY shares.
So that arbitrage argument doesn't hold for SPX. But arbitrage is what makes prices sane, I get a little uncomfortable when it doesn't hold.
Maybe the whackiness demonstrated below just doesn't matter. Maybe I'm having a brain freeze. So wanted to ask for a double check of my thinking.

Below are some snippets of a SPY options chain with IV, and then a SPX options chain with IV:

7/27/2024: SPY 544.22
expiry April 17 2025 ITM SPY puts:
strike 570 bid 33.03 ask 34.24     IV 570-544.22 = 25.78: bid and ask greater than IV
strike 580 bid 38.99 ask 40.54     IV 580-544.22 = 35.78: bid and ask greater than IV
strike 590 bid 46.17 ask 47.94     IV 590-544.22 = 45.78: bid and ask greater than IV
strike 600 bid 54.69 ask 56.72     IV 600-544.22 = 55.78: ask greater than IV
strike 610 bid 64.41 ask 66.66     IV 610-544.22 = 65.78: ask greater than IV
strike 650 bid 104.30 ask 106.79   IV 610-544.22 = 105.78: ask greater than  IV

CONCLUSION:
SPY ask is always greater than IV.
This makes sense because otherwise there'd be "free money", i.e. if you held SPY shares and if the ask were less than the IV then you could buy that put and pocket the difference i.e. an arbitrage opportunity.

Now look at SPX:

7/27/2024 SPX 5459
expiry April 17 2025 ITM PUTS:
strike 5700 295.50 298.10 IV 5700-5459 = 241: bid and ask greater than IV
strike 5800 342 345.30 IV 5800-5459 = 341: bid and ask greater than IV
strike 5900 386.70 410.70 IV 5900-5459 = 441: bid and ask NOT greater than IV
strike 6000 447.80 471.80 IV 6000-5459 = 541: bid and ask NOT greater than IV

CONCLUSION:
SPX ask is not always greater than IV: it is for nearer ATM strikes but is not for more ITM put strikes

You can't hold, i.e. buy or sell SPX shares, so the arbitrage argument for SPY doesn't hold for SPX.
But arbitrage is what generally keeps market prices sane.
So I was a little surprised to see the lack of arbitrage to keep a SPX 'ask' in a sane relation to IV.
It just doesn't matter if it's not sane (given no "shares" to buy or sell)?
I was also suprised that the SPX bid/ask didn't have a more uniform relation to SPY bid/ask.

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