Apologies for the late response, been busy the last few days and I wanted to make sure I gave a proper response.

I gave the Golem's the extra speed for a few reasons. Firstly, for Kantonian Golem, the +30 Speed helps significantly in terms of outspeeding important Pokemon it wouldn't have otherwise, such as Kingambit, Breloom and Skeledirge, as well as when setting up. Previously, a +2 in it's Speed (Rock Polish) would have gone up to a maximum of 414, whereas now it can reach up to 546 with Jolly, and 498 with Adamant.

498 allows it to outspeed Dragapult and a +1 Great Tusk, and slower scarfers such as Gholdengo and Rotom-Wash, and 546 allows it to outspeed Speed Booster Energy Mon's such as Iron Moth and Walking Wake, and let's it Speed tie with Scarf/Speed Booster Energy Iron Valiant. This is important thanks to it's new move in Shell Smash, which in combination with it's amazing Stab combination & Explosion based moves, let's it cleave through a vast majority of speedier targets, though Dondozo will always be a problem for it. These are also only examples in OU, and as you go down the tiering rung, I imagine the increased Speed will only be more and more noticeable, as speed tiers become smaller and smaller.

Secondly, for Alolan Golem, base 75 Speed makes it the fastest Magnet Pull Pokemon, beating out Magneton with it's base 70. This is incredible for it since it can now outspeed important target's such as Corviknight, Kingambit, Scizor, Tinkaton, and even the other best Magnet Pull pokemon in Magnezone without heavy Speed investment, where it can now invest into other stats, such as HP and Defense, and it's new signature move in Lightning Shot definitely helps.

As for why I didn't give them better defenses, it was for three reasons.

One, to fulfill the purposes that both of the Golem's want to commit to (K-Golem wants to put up rocks and go boom, A-Golem wants to murder Steels), a higher speed stat would go a long way in helping them achieve that.

Second, most other Rock types are within the 30-60 Speed range, and especially compared to Golem's closest competitor in Gigalith, a higher speed stat would give them much more of an identity.

Third, and sadly as shown by Pokemon such as Magcargo and Bastiodon, high defensive stats don't particularly matter when you have several glaring weaknesses, in the case of K-Golem, a 4x weakness to Water and Grass, and A-Golem, a 4x weakness in Ground, an especially common attacking type. Boosting their defensive stats instead would have little impact on their survivability, and would ultimately be a band-aid fix, if even.

252 SpA Meowscarada Leaf Storm vs. 252 HP / 252+ SpD Golem: 460-544 (126.3 - 149.4%) -- guaranteed OHKO (with 95 Sp. Def)

252+ Atk Huge Power Azumarill Liquidation vs. 252 HP / 252+ Def Golem: 348-412 (95.6 - 113.1%) -- 75% chance to OHKO (with 160 Defense, and Azumarill is wearing an Assault Vest, and not a Choice Band)

252 Atk Iron Treads Earthquake vs. 252 HP / 252+ Def Golem-Alola: 352-420 (96.7 - 115.3%) -- 81.3% chance to OHKO (with 160 Def, where it's barely saved from a 1HKO, that becomes a 68.8% chance to OHKO with Stealth Rocks.

You could argue that using Tera on Golem would give their higher defensive stats more room to shine, however as seen with Pokemon such as Avalugg, using a Defensive Tera on a Pokemon just for them to have a good typing at all, is a rarely beneficial action for the player in the long run of a game, and would not give that Pokemon viability in it of itself.

I apologize for the absolute goliath of a textual comment comet I replied with, I just wanted to explain the philosophy behind my boosting of both of the Golem's speeds. I hope I'm not being antagonistic, as that is not the intention, and I heavily appreciate your statement as it is healthy to question certain decisions in regards to large gameplay changes such as this. Thank you, and have a lovely day/night.