The Rambam in Hilchos Melachim 3:2 writes how a king can't have more than 18 wives:
לֹא יַרְבֶּה לוֹ נָשִׁים. מִפִּי הַשְּׁמוּעָה לָמְדוּ שֶׁהוּא לוֹקֵחַ עַד שְׁמוֹנֶה עֶשְׂרֵה נָשִׁים בֵּין הַנָּשִׁים וּפִלַּגְשִׁים הַכּל שְׁמוֹנֶה עֶשְׂרֵה
"He must not have too many women" (Deut. 17:17). By Tradition we have learned that he may have up to eighteen women including wives and concubines.
However in the subsequent 2 halachot the Rambam writes how a king may not own more horses or gold/silver than he may need.
Unlike the number of wives a king may have, why isn't a specific number given for the amount of horses and gold/silver that a king may own?