Mixtapes and releasing an album is two different things.
Ask the "Drama King" Kay Slay about the mixtape game.
Now, being that this sampling issue is becoming of increasing concern, check the following piece of info...
expectations were high for Biz's next album, I Need a Haircut. "Sales were already disappointing" when Biz was served a lawsuit by Gilbert O'Sullivan, who claimed that the album's "Alone Again" featured an unauthorized sample from his hit "Alone Again (Naturally)." O'Sullivan's claim was upheld in a ruling, Grand Upright Music, Ltd. v. Warner Brothers Records, Inc., that altered the landscape of hip-hop, finding that all samples must be cleared with the original artist before being used. In accordance with the ruling, Warner Bros., the parent company of Cold Chillin', had to pull I Need a Haircut from circulation, and all companies had to clear samples with the samples' creators before releasing the records. This development mirrored the increasing popularity of hip-hop and the financial stakes over which releases were set. Biz responded in 1993 with the mischievously titled "All Samples Cleared!", but his career had been hurt by the publicity emanating from the lawsuit, and the record suffered accordingly.
You don't expect to sell but "X" amount on the first album, okay fine.
But if it catches on or you go on to do a second, third joint and blow up, then people start checking for your first joint, and you exceed those first numbers, then what????
Releasing an album with well known samples can be costly given the right circumstances.