Dandelion or Dandelion++ was not implemented in Bitcoin because few bitcoin devs thought it could result in DoS attacks: https://bitcoin.stackexchange.com/a/81504/
I was reading the blog post https://sethsimmons.me/posts/moneros-ongoing-network-attack/ which has almost all the details about recent DoS attacks on Monero.
It's mentioned that Dandelion helped in making it difficult to link IP with transactions but did Dandelion help the attacker in DoS attack?
The referenced blog post is a little misleading insofar as it wasn't the actual introduction of Dandelion++ that enabled or started the recent DoS attacks, merely that the attacks ramped up around the same time as Monero performed a major release, for which amongst other things also happened to include Dandelion++. Anecdotally, major releases are of course ideal times to launch such attacks.
The blog post does however give a good timeline and links to the PRs that have been plugging the holes used in the various and changing attacks and one should note that only 2 of the PRs even mention Dandelion++; many of the weaknesses this attacker has been exploiting preexisted this latest release (v17).
Luckily these attacks, whilst annoying, are fairly harmless (i.e. no funds are at risk and the network is still operating), so the net result is actually strengthening Monero. So whilst of course responsible disclosure would have been preferred, better to have manageable attacks now than left to exploit another day, possibly with greater impact.
Lastly, I'd caution using Bitcoin as a reference as to why something is or isn't added to Monero. Many things proposed and rejected for Bitcoin have found a place in Monero (privacy for starters). That said, it's worth noting that it was Dandelion, not Dandelion++, that was originally proposed for Bitcoin and there were various objections, most unrelated to possible DoS attack vectors.
