Why do you think so? I will state why I said that. First of all, yes it is difficult for them, and yes being Catholic with access to the sacraments is the royal road, filled with grace and meeting Christ in the flesh every Sunday. Who does not love to be united body and soul to the Lord? For this alone conversion efforts should be made as if it is a life and death issue (because it matters more than all things). BUT it is still possible for atheists to be saved, and not the least reason is that God can do what He wants, and desires the salvation of all, and does not give salvation based on foreseen merits, but only based on His grace and love for the elect (no action, even being Catholic and following the teachings in soul and body, is inherently meritorious of salvation without God first deciding to make it so based on His love for the person doing it, which is never based on anything they did or will do, only on Him.)
Refusal to believe or acknowledge God is an objective mortal sin, but if not done with full knowledge and deliberation it is not an actual mortal sin, therefore not violating the state of grace. Baptism is required for salvation, but there are three (water, blood, desire), an atheist may have an implicit desire for the third of the truly love their neighbors which is always ordered toward God (imago dei, 1 John 4:20-21), pope Pius XII: “An act of love is sufficient for the adult to obtain sanctifying grace and to supply the lack of baptism.” If they commit an actual mortal sin they can return to the state of grace by the same kind of act of love, or sincere regret over their wrongdoings not out of attrition but because they know it was unjust, even if they do not recognize God as Justice itself (God is Mercy, Justice, Truth, Love, Beauty, anyone who seems these things with a whole heart and not selfishly seeks God, even if they do not know it is God they seek, see divine simplicity). Even if someone rejects the Church, and knows of it, they can be saved and joined to it, therefore “no salvation out side the church of Christ” is preserved, see St. JP2: The axiom means that for those who are not ignorant of the fact that the Church has been established as necessary by God through Jesus Christ, there is an obligation to enter the Church and remain in her in order to attain salvation (cf. LG 14). For those, however, who have not received the Gospel proclamation, as I wrote in the Encyclical Redemptoris Missio, salvation is accessible in mysterious ways, inasmuch as divine grace is granted to them by virtue of Christ’s redeeming sacrifice, without external membership in the Church, but nonetheless always in relation to her (cf. RM 10). It is a mysterious relationship. It is mysterious for those who receive the grace, because they do not know the Church and sometimes even outwardly reject her . It is also mysterious in itself, because it is linked to the saving mystery of grace, which includes an essential reference to the Church the Savior founded. " therefore, atheists can be saved, and in my opinion, many a probably saved. We shall know when we see God.
God bless and may St. Joseph intercede for us, so we may all see God.