Reasons for not claiming forks:
1. Because it's practically worthless compared to Bitcoin- Bitcoin is $5000/coin... BTG is $18/coin... unless you had substantial BTC holdings... the amount you stand to gain is miniscule
2. It's not worth the hassle- If you had BTC in Electrum, it is relatively simple... move coins to new wallet, download the appropriate Electrum fork (like Electron Cash) use old seed and get instacoins... however if you had it in Bitcoin Core, you'd need to go through the hassle of moving all your coins, then syncing the full blockchain for "Core" wallets of the new fork... or exporting your keys and then find a wallet that you can import keys etc... or if your coins were in a paper wallet you'd need to generate new paper wallets... or if your coins were in cold storage you'd need to reorganise everything... for $18/coin
3. It's not worth the risk- Downloading "unproven" wallets, moving coins around from cold storage, exporting and importing seeds/private keys etc... there is a certain level of "risk" involved... for a coin worth $18... is it worth it?
For the record, I've used:
Bitcoin ABC (Bitcoin Cash "core" wallet)
Bitcoin Gold Core
ElectronCash
ElectrumG (Bitcoin Gold "Electrum" wallet)
Electrum BCD (Bitcoin Diamond "Electrum" wallet)