The gloptop version of SMB/DH is far more common than the chip version. Years ago I bought around 175 SMB/DH carts for recycling, and that yielded maybe 30 boards with DIP ICs. You can tell without opening by looking at the connector, on the gloptop version the unused pins just aren't there. There are also label variations, the older ones (without a seal of quality) tend to be chip versions, but not always.
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So if its cheap, why aren't all carts like this?
If you look at the carts made today (pirate and unlicensed Fami carts I mean), I'd be surprised if there were any that use actual removable chips. On one cart I had (came with the PowerJoy II) actually the board was made to take a DIP ROM, but the ROM was a gloptop installed on a DIP-sized carrier board, I thought that was pretty funny.
(mapper chip was a blob too of course)
I guess it wasn't common with other games because of a higher set-up cost.