Why is the sperm of a guy thick?
The sperm are not thick. Semen — the chalky to milky white, semi-viscous fluid that is ejaculated — contains sperm plus fluids from the seminal vesicles (almost 1/3 of the volume) and the prostate (about 2/3 of the volume) make up almost all of the volume of the semen. Sperm make up about 1% of the volume of the semen.
These fluids cause the thickness.
The Copwer's gland also adds some volume to the semen. However, during excitement and before ejaculation, it can slowly release a clear, semi-viscous fluid that neutralizes the acid content from urine and act as a lubricant. Although this fluid can contain some sperm, the number of sperm is too small to have much danger of pregnancy.
I hope this helps. Thanks for asking.