> If the Supreme Court does not hear a case, it is tacitly saying it agrees with the lower court's decision.
No, it's not, which is why denials of cert. do not elevate the lower court’s decisions to the precedential effect of a Supreme Court decision.
The Supreme Court takes a very limited share of the cases offered to it in its discretionary jurisdiction each term, and the factors involved in those decisions typically include whether or not there is a split between the Courts of Appeals on the question raised and the degree to which Court perceives the case to be one of national importance among other factors, the decision is not centrally about the merits of the case.
Also, Roe v. Wade was not the first abortion-law case to come before the Supreme Court, just the first to raise and be decided on the question of whether abortion itself was protected. Other challenges were on different grounds, e.g. U.S. v. Vuitch (1971) unsuccessfully challenging Washington, D.C.’s abortion law (which had maternal health exceptions) for unconstitutional vagueness. Most lawyers prefer to argue things which are established in law rather than novel theories (because trial courts aren't prone to accept novel theories, because clients get a lot better result being cleared by a trial court than exhausting appeals through the State and then appealing to the appropriate federal courts, and for other reasons.)