The most obvious answer to the question is that Bitcoin is not Ether or the other way around, depending how you want to put it.
The other difference is Bitcoin is POW while Ethereum is POS, which can make a big difference. On the Bitcoin network, there is a 3rd party involved that doesn't exist on Ethereum anymore - miners.
Another difference is that the max supply of Bitcoin is known, while Ether keeps getting printed... and burned (which can make it either inflationary or deflationary - currently, it is deflationary).
You can destroy bitcoins, but it's not as easy as sending them to @null, as we are used to in (D)POS consensus mechanisms. But you can lose keys to wallets, have devices where early coins were mined and stored lost or destroyed, which is effectively the same thing.
There is more development in and around Ethereum than it is for Bitcoin. Other chains forked Ethereum code or use EVMs, which make them potential candidates for future spot ETFs. Same for a few forks of Bitcoin if there is interest.
There is also the advantage of being the first to the market and having a name that is sometimes used to refer to the entire space by non-initiated.
The way approvals came for the two sets of spot crypto ETFs marks a difference too.
For spot Bitcoin ETFs, it was a long process, the SEC gave in little by little, but approvals became obvious after a certain point.
A clear distinction that one should keep in mind: all spot Bitcoin ETFs applications were cleared to operate practically immediately after they were approved on the exchanges. I remember I was surprised then that there was no time between approvals on the exchange and starting of trading.
For spot Ethereum ETFs, the indications were toward a hard no (so, denial), until the final week, when the SEC requested an emergency update of the filings. Then it became quite clear they will be approved.
The SEC was forced to approve exchange listings for spot Ethereum ETFs by the deadline. What didn't happen yet was to clear any of the spot Ethereum ETFs to operate. Something that for spot Bitcoin ETFs took something like a day, at most, if I remember well.
So the SEC is dragging its feet with these final steps. They could come tomorrow or in a month. Nobody without inside information has any idea when it will happen. They have no deadline on this.
So, to say spot Ethereum ETFs have been approved is only half-true. Theoretically, the approval process started when exchange trading was given the green light, and it is unlikely to be stopped, but it will end when the spot Ethereum ETFs will be approved to operate (to handle clients' funds).
At this point, I am curious if it only takes a few more days or a few more weeks. I wouldn't want to speculate since there are major interests at play that can influence this decision, if they want to.
Want to check out my collection of posts?
It's a good way to pick what interests you.