While you are right that FSH activity is also needed:
'A number of studies suggest that FSH rather than LH plays a crucial role in stimulating spermatogenesis (i.e. DNA synthesis in
spermatogonia and preleptotene spermatocytes) indirectly through the FSH receptor in Sertoli cells. Fifteen of 28 patients (54%) enrolled in our hormonal treatment protocol showed decreased FSH levels (i.e. FSH reset) after hCG treatment'
https://oup.silverchair-cdn.com/oup...DqNV9NUDPQ__&Key-Pair-Id=APKAIUCZBIA4LVPAVW3Q
While, as expected, LH and FSH levels are TEMPORARILY reduced during HCG administration
don't forget that HCG has LH, along with some FSH activity on its own
Merck says so in the Pregnyl insert, and there are studies that prove it
'The action of HCG is virtually identical to that of pituitary LH, although HCG appears to have a small degree of FSH activity as well.'
https://www.merck.com/product/usa/pi_circulars/p/pregnyl/pregnyl_pi.pdf
To properly recover both Testosterone and fertility you need them all:
1 LH
2 FSH
(HCG provides activity mimicking them both, at an affordable price, unlike pricey recombinant LH and FSH)
3 High enough doses
4 Long enough time
In a nutshell (no pun intended lol)
with 20000 IUs you had plenty LH/FSH activity yet you are still missing #4: enough time
Studies show HCG is a safe (just watch for excess Estrogen) long term drug:
Therapy with human chorionic gonadotrophin alone induces spermatogenesis in men with isolated hypogonadotrophic hypogonadism--long-term follow-up. - PubMed - NCBI
studied for 14-120 months (up to 10 years!)