The pick block function doesn't work with mob spawners

you aren't supposed to be able to do that, mojang actually had it enabled with the normal pick block in the first snapshot it introdused, but later removed the ability to do that.
works as intended

Do you know why Mojang removed this ability? I can't see any resone why.

people were able to achieve the 52 by doing it and Mojang don't want us to.

Is this still a concern in the current Minecraft version 14w18b / Launcher version 1.3.11 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Confirmed for 14w18b, but I'm pretty sure this is Working As Intended. As I'm not a mod I can't make that decision but it seems pretty obvious Mojang doesn't intend mob spawners to be pickblock-able. Btw custom spawners can be made by using the setblock command in a command block. Here's a simple one:

/setblock ~2 ~1 ~0 mob_spawner 0 replace {EntityId:Zombie}

Here's a not so simple one:

/setblock ~-1 ~-1 ~0 mob_spawner 0 replace {EntityId:Zombie,SpawnData:{Equipment:[{id:276},{},{},{},{id:397,Damage:3,tag:{ench:[{id:1,lvl:4}],SkullOwner:RageLokiCat}}]},SpawnPotentials:[{Type:Zombie,Weight:1,Properties:{Equipment:[{id:278,tag:{ench:[{id:20,lvl:2},{id:21,lvl:10}]}},{},{},{},{id:397,Damage:3,tag:{SkullOwner:MHF_Herobrine},Count:1}]}},{Type:LavaSlime,Weight:1,Count:4},{Type:Blaze,Weight:1,Count:2},{Type:CaveSpider,Weight:1,Count:8},{Type:Skeleton,Weight:1,Properties:{Equipment:[{id:261,tag:{ench:[{id:50,lvl:1}]}},{},{},{},{id:397,Damage:3,tag:{ench:[{id:0,lvl:2}],SkullOwner:MHF_Spider}}],Riding:{id:"EntityHorse",Type:4,Tame:1,SaddleItem:{id:329,Count:1,Damage:0}}},Count:2},{Type:Zombie,Weight:1,Properties:{Equipment:[{id:283,tag:{ench:[{id:20,lvl:2},{id:21,lvl:10}]}},{id:301},{id:300},{id:299},{id:397,Damage:3,tag:{ench:[{id:1,lvl:4}],SkullOwner:MHF_LavaSlime}}]},Count:2},{Type:Skeleton,Weight:1,Properties:{Equipment:[{id:261}],Riding:{id:"Blaze"}},Count:2},{Type:Skeleton,Weight:1,Properties:{Equipment:[{id:261},{id:317},{id:316},{id:315},{id:397,Damage:3,tag:{ench:[{id:1,lvl:4}],SkullOwner:MHF_Villager}}],Riding:{id:"Slime",Size:4}},Count:1},{Type:Zombie,Weight:1,Properties:{Equipment:[{id:283,tag:{ench:[{id:21,lvl:10},{id:34,lvl:3}]}},{id:301},{id:308},{id:299},{id:397,Damage:3,tag:{ench:[{id:1,lvl:4}],SkullOwner:MHF_Pig}}]},Count:5},{Type:PigZombie,Weight:1,Properties:{Equipment:[{id:283,tag:{ench:[{id:21,lvl:10},{id:34,lvl:3}]}}],Anger:1},Count:4},]}

Note that a recent snapshot changed custom head codes. They'll all be steve heads if broken (or if there's no internet connection). Also I hear the anger tag for zombie pigmen was broken in another recent snapshot (last AI change).

Affects 1.18

Affects 22w16b

Affects 22w43a, despite spawners being added to the creative inventory

Apparently fixed in 22w44a according to patch notes

Can confirm fixed in 22w44a.